Wikipedia:Reference desk/Science

May 14

When is it first clear that a child is left or right-handed?

I was wondering when it was first obvious that a child is left or righthanded. The article on right-handed has nothing on it. Capitalistroadster 02:46, 14 May 2007 (UTC)

I don't know, but the results of this google search might be helpful: first age handedness children. Anchoress 02:50, 14 May 2007 (UTC)

When they've been writing or painting for a few months it's obvious. Before that - it's really hard to tell. SteveBaker 03:46, 14 May 2007 (UTC)

My son could throw a ball at approx 10 months old. Surely you can tell then? Sandman30s 09:49, 14 May 2007 (UTC)

My son was using both hands equally for almost all activities - until he started drawing and painting - for which he used only his right hand. If you put a crayon into his left hand, he'd pass it over to his right and then starts doodling. I don't think a ball toss is sufficiently strongly associated with laterality to show a preference at early age. But hey - we're all individuals and handedness isn't a 'pure' left/right thing. There are degrees of the strength of preference - so it's possible you could tell earlier. SteveBaker 11:32, 14 May 2007 (UTC)

Even at that age I am fairly sure he used to pass the ball over to his right hand if it was in his left. Certainly, at age 12 months he was running, picking the ball up with eaither hand, and throwing with his right. Also kicking with his right foot. Being right-handed myself, I find it very unnatural to attempt a throw with my left. I think he would have found the same even at that age. Also early activities such as building blocks or opening a container etc. - way before drawing or painting. Sandman30s 12:19, 14 May 2007 (UTC)

The child would probably experience the preference well before the parents were aware of it. The question is when is it first clear, presumably meaning "clear to the parents". One of my sons is left-handed. We first noticed it when he was around 12-15 months. My mother was quite worried that he was not quite normal, as he was the first person from either side of the family in at least 2 generations who showed a preference for the left. I had to reassure her that it's quite ok to be left-handed, and had to resist her attempts to make my wife and me make him use his right hand over his left. JackofOz 12:43, 14 May 2007 (UTC)

insect identification

I found these guys on my windowsill today: [1] [2] [3] [4]. Does anyone know what they are? Jay Gatsby^(talk) 02:47, 14 May 2007 (UTC)

Unfortunately, all 4 pics appear to be out of focus. StuRat 02:58, 14 May 2007 (UTC)

It's the best I could do with my camera right now (the insects are really small). Care to take any guesses? Jay Gatsby^(talk) 03:01, 14 May 2007 (UTC)

I think they may be termites. What do you guys think? Jay Gatsby^(talk) 03:08, 14 May 2007 (UTC)

That's what they look like. Assuming I wasn't wearing my glasses at the time that is. If they are on your sill, you should call an extermination expert forthwith. --BenBurch 03:11, 14 May 2007 (UTC)

Thanks for your opinion. I think I can get better pictures tomorrow afternoon when there is more sun. To be continued! Jay Gatsby^(talk) 03:21, 14 May 2007 (UTC)

I don't think you need more Sun, I'd guess you need to hold the camera farther away or adjust it for a closer focus. StuRat 04:24, 14 May 2007 (UTC)

If you look at this image, there's really not much room for doubt (your guys look like the workers, not the toothy soldiers). I'd call a bug man. --TotoBaggins 03:51, 14 May 2007 (UTC)

You need to see if your camera has a 'Macro' setting - that's what's needed to take photos with the lens closer than maybe a foot or so to the subject. Most halfway decent camera have a macro option. SteveBaker 11:34, 14 May 2007 (UTC)

Sigma Replication

What is Sigma Replication? —The preceding unsigned comment was added by 59.93.16.61 (talk) 04:51, 14 May 2007 (UTC).

I don't know, but a google search with "sigma replication" has a few likely looking sites. The first hit's abstract ([5]) suggests it is a "mode of bacteriophage lambda DNA replication during its lytic development in Escherichia coli cells". The introduction of that paper would be likely to have a more precise description. Aaadddaaammm 08:09, 14 May 2007 (UTC)

Were you unable to access the article? Quoting from the article:

"rolling-circle (σ) replication occurs late after infection to produce long concatemers that serve as substrates for packaging of λ DNA into phage proheads. The mechanism regulating the switch from θ to σ replication remains unknown."

Someguy1221 09:15, 14 May 2007 (UTC)

Speeding up the aging process in paper

Does anyone know how aged parchment and paper can be reproduced chemically. I make reproduction lithographs as a hobby and would love to be able to print them on subtly toned paper. I know all the coffee and tea techniques but unsurprisingly they all stink of um, coffee and tea! I thought that I heard of a technique using alum that changes the cellulose in some way? Any information would be greatly appreciated even if it is completely unverified.

Thanks - Kirk UK —The preceding unsigned comment was added by 82.153.110.133 (talk) 07:19, 14 May 2007 (UTC).

High doses of UV light and acidic humid environment? --antilived^{T | C | G} 07:42, 14 May 2007 (UTC)

It depends on whether you want to replicate the phenomenon or the appearance. You can buy "old-style" paper or parchment at an art-supply store. Nimur 13:32, 14 May 2007 (UTC)

I would think they would normally just use yellow dye, since most people want it to look old, but don't actually want it to be as fragile as such an old document would really be. StuRat 14:33, 14 May 2007 (UTC)

Since this is a hobby anyway, you might as well go all out and make your own paper. You can control the size of the fibers, the thickness and density (though you might find an upper limit to you ability to press the pulp using just hand clamps and weights lying around the house; the handmade paper I have seen tends to be closer to wedding stationary than onionleaf), and even the composition (bamboo and cotton are both readily shredded for pulp). Papermaking is a good place to start. Failing that, might storing the paper you have in a warm, dry, well-ventilated area for a week or two get rid of the smell? Eldereft 03:21, 15 May 2007 (UTC)

It's traditional to rub damp tea leaves on paper to make it look old.

"Wedding stationary" may explain why a lot of marriages end in divorce. If only they'd used stationery instead.  :) JackofOz 02:40, 17 May 2007 (UTC)

Agreed, who would want a stationary wedding ? Don't most people (well, most women, anyway) prefer a moving ceremony ? StuRat 05:27, 18 May 2007 (UTC)

heh, oops. Shows what I get for relying on Firefox's inline spellchecker instead of actually reading. :) Eldereft 03:36, 17 May 2007 (UTC)

Atlantis

What is your opinion on the existence of Atlantis? Do you think a super continent existed in which Atlantis resided? Do you think that the Altantians had a hand in the Eqyptian Dynasty? --Juliet 13:53, 14 May 2007 (UTC)

Since this question calls for opinion, I've answered here: [6]. StuRat 14:27, 14 May 2007 (UTC)

No, Atlantis could not have had it's own continent or supercontinent. If it existed around the time that is normally said it had existed. That's not an opinion. [Mac Δαvιs] ❖ 19:05, 14 May 2007 (UTC)

As far as I know, Atlantis does exist, and resides in North America except when it's in orbit. Nimur 01:45, 15 May 2007 (UTC)

which egyptian dynasty? They've had at least 30.

you don't wan't to go to atlantis, they're all just pompous, *****ing, self obsessed ***s :] HS7 16:28, 16 May 2007 (UTC)

And no it doesn't exist, they would have found it overwize :( HS7 16:34, 16 May 2007 (UTC)

I've heard of being "too smart for your own good", but can one be over wize ? StuRat 23:39, 16 May 2007 (UTC)

HS7, are you a reincarnation of Charles H. Duell? JackofOz 02:38, 17 May 2007 (UTC)

Glass

Hi my chemistry teacher has given me this question "Why is glass described as a supercooled giant covalent liquid?" and I can not find any explanations or information on Google, can anyone help me out?

The glass (window glass) is a silicate of potassium and sodium. If it cools down and finds its way to the termodynamical best point it would form crystals. But molten and cooled to room temperature (supercooled) the crystalization is not possible any more. Liquid is false, because the viscosity of glass is really high, even in centuries the glass windows do not get thicker at the bottom (even if many people tell this story). So its more a supercooled amorphous solid.--Stone 14:12, 14 May 2007 (UTC)

Read the Pitch drop experiment for insight to a similar material! Nimur 15:07, 14 May 2007 (UTC)

To augment Stone's answer, you may be interested in reading our article on glass as a liquid. — Lomn 18:12, 14 May 2007 (UTC)

Apparent Mass vs. Invariant Mass

I have been reading several Wikipedia pages involving the effects of relativity. Now, I have read that as your velocity increases, your mass increases. After some more reading, I found that this was misleading; the object's mass stays the same from it's viewpoint, but it's mass as viewed by other observers (called relativistic mass) increases. But, we know for a fact that the number of atoms inside that speeding object has not increased.

My question: how do both reference frames (the speeding object and the observer at rest viewing that object) observe/interpret this increase in apparent mass? And what are the consequences for this increase in apparent mass?

Thanks in advance. =) —The preceding unsigned comment was added by 129.115.251.49 (talk) 16:57, 14 May 2007 (UTC).

A primary consequence of the relativistic mass is the change in inertia, apparent to outside reference frames. As you know from Newtonian mechanics, F=dp/dt, that is, the force applied to an object is proportional to the time derivative of momentum, However, here momentum is not merely mass times velocity, but is magnified by gamma (1/(1+(v/c)^2)^.5) (I need to figure out the math functions on here). And so a very strong force applied to an object that is passing you at relativistic speeds will appear to deflect its trajectory much less than you would expect using Newtonian mechanics. The observer on the fast moving object sees its trajectory altered by the normal classical calculations, but his reference frame is experiencing time at a much slower rate. For this reason, the observations don't conflict, you see the trajectory altered very slightly, and he sees the same alteration at such an accelerated rate that it appears normal (classical). I hope that made sense. Someguy1221 17:40, 14 May 2007 (UTC)

If I'm reading this right, I think you're confusion comes from assuming something along the lines of mass just meaning how many atoms are inside something. Sorry if I'm reading this wrong. Atoms have mass, and different atoms have different masses. The masses that we use for atoms, in everyday physics and chemistry, are their masses when they are stationary relative to us. When an object's velocity increases relative to us, its mass also increases relative to us. This means the atoms gain mass, not that there are extra atoms. Skittle 18:03, 14 May 2007 (UTC)

Yes, I was aware that the number of atoms remains the same but the mass per atom increases; I guess what I'm asking is that, if the observer views that the moving object has gained mass, wouldn't the observer also see that that object now exerts more gravity on the matter around it? But, on the other hand, from the point of view of the moving object, how would you explain the increased in gravitational effects you experience as your velocity increases, despite the fact that your mass has not increased from your point of view?

Sorry if I'm bad at phrasing questions...but I appreciate the responses so far! =) N3rday 18:37, 14 May 2007 (UTC)

Consider testing the gravity of a moving point particle by placing a (vanishingly small) test mass adjacent to its line of travel, so close that the gravitational force is non-negligible only for the moment of closest approach. We can then, accounting for how slowly the attracting mass was moving (thus how long the "moment" was), derive its inertia by noting the velocity of the test mass after the encounter. The same attractor at different speeds will give different resulting velocities, but an observer on the attractor will claim that the velocities are all the same and we are merely measuring them with varyingly slow clocks! Dealing with kinematics in special relativity is always difficult because the very definitions of such basic quantities as velocity contain variables (that is, time and length) that depend on who measures them. I believe this improves somewhat on Someguy1221's discussion of the non-gravitational case: it's not that anyone's observations of some objective reality are accelerated but rather that there is no objective reality and anyone's observations can be explained by someone else as resulting from "measurement errors".

Also, note that, say, a magically-powerful rocket has less inertia at 0.9c than it did at rest, because it has left so much fuel behind. So to really see this effect you'd have to constantly supply new mass to the rocket, at which point it's not so mysterious that the resulting mass-energy (in either form) has more inertia. Does that help? --Tardis 20:30, 14 May 2007 (UTC)

Yes, actually, that does help quite a bit. On a similar subject, do you know of any good literature to familiarize myself with relativity? It seems like I should just read up on it and gain knowledge to answer my own questions rather than crowding the Reference section of Wikipedia...thanks for helping a physics newbie understand. N3rday 04:25, 15 May 2007 (UTC)

I read a book The Meaning of Relativity by an "A. Einstein" who seemed to know what he was talking about. It was published by Princeton. There are of course many many other books on the subject; if you like that author, he also wrote Relativity: The Special and General Theory with a more technical bent, which is available at Wikisource. Re: thanks: you're welcome! --Tardis 16:04, 16 May 2007 (UTC)

Orchids

I bought two orchids two years ago and they had beautiful flowers on them. Eventually the flowers fell off but never came back. The plant is still alive but how do I make them flower again? --Juliet 18:17, 14 May 2007 (UTC)

That seems to be a very common experience with orchids. Unfortunately, there is no real easy answer. There are an incredible variety of orchids, and they each may need different conditions in which to reliably bloom. From my own experience, I recommend these things, which have worked fairly well for me:

-Water consistently, never letting them dry out

-Experiment with different lighting conditions - keep them in one place for a month or two to see if anything happens before trying another spot

-Use fertilizer that is specific for orchids, often called simply "orchid food"

-Transplant to a larger container if the roots seem crowded and/or tangled

Even when you put the orchid in its ideal conditions, it may take months for it to start to bloom. It will slowly grow a new stalk for the flowers. But once it gets blooms, they generally last a long time. With orchids, patience is key. Hope this helps, at least a little. --Ed (Edgar181) 18:48, 14 May 2007 (UTC)

A google search for "making orchids flower" found some causes listed here including: Not enough light, poor soil, not enough temperature fluctuation, poor water. See the referenced site for more details. The one thing not mentioned above is the need for about 7 - 10 degrees F ( 4-6 celsius) change in temperature between night and day.Good Luck! --Czmtzc 18:50, 14 May 2007 (UTC)

Juliet, could you please say what kind of orchid are you asking about? I'm afraid there's too little information in your question as it is. Some orchids need winter rest, some don't. Some orchids need bright light to flower, some don't. Some are more tolerant to "bad" water than the others. Some are more sensitive to air quality (humidity, stove gas, air motion) than others. Each orchid has its preferred temperature range. So, could you please specify what kind of orchid is it? Cheers, Dr_Dima.

Just be patient, flowers don't always bloom every year. Vranak

The Celestine Prophesy

The Celestine Prophesy

Is the idea of Synchronicity and the Insights described in the novel The Celestine Prophesy can happen or is there just way too much anger, hate, fear in the world for this to happen? --Juliet 19:45, 14 May 2007 (UTC)

The idea of synchronicity is that an apparent "coincidence" has some deeper meaning, and is not just a coincidence. These occurrences would take place regardless of there being anger, hate, and fear. The insights of The Celestine Prophecy, however, will almost certainly never occur, because it is spiritualistic mumbo jumbo. − Twas Now ( talk • contribs • e-mail ) 21:05, 14 May 2007 (UTC)

Sleeping Face-up

Why do I find it hard to sleep facing up (also known as supine position)?

The only conscious idea I can come up with is that I feel vulnerable.

Maybe fearing someone will hit me in the face, neck, organs/stomach, and genitals?

Is there another, deeper reason why it may be hard for me?

And how common is it that people find it uncomfortable to sleep in the position? PitchBlack 20:28, 14 May 2007 (UTC)

There can be lots of reasons. It could be tied to you being born at a time when parents were recommended to lie their babies on their fronts to sleep, since that was thought to reduce the risk of cot death. Since this was later found to increase the risk, the advice was reversed, however I know many people in that age group who prefer to sleep in a more 'face-down'y kind of way, while people I know who were laid on their backs as babies tend to prefer sleeping in a more 'face-up'y sort of way. But this is OR :-) On top of this, curling up is a protective position, so if it is sleeping straight, compared to sleeping curled up, that you find hard, vulnerability could be a factor. Skittle 21:10, 14 May 2007 (UTC)

Do you have allergies? Sleeping on one's back can be very uncomfortable during allergy season because of post-nasal drip. Sorry to be gross. --Trovatore 21:25, 14 May 2007 (UTC)

Your weight and the way it's distributed in your body, the type of mattress and pillow, and whether you have trouble with your back, neck, stomach, etc., can all influence which sleeping positions are comfortable. Also if the room is not completely dark, you may want to sleep facing away from the light source. It is possible that there are medical or psychological issues, which would be beyond the scope of the reference desk. --Anonymous, May 14, 2007, 21:30 (UTC).

I've never been comfortable sleeping on my back (or front). (Is this OR? :-) ) I always curl up, on one side or the other. This is an area where different people are just different, I think. Unless you don't have any positions that are comfortable, I wouldn't worry about it a bit. —Steve Summit (talk) 23:34, 14 May 2007 (UTC)

Obstructive Sleep apnea can be more of a problem for people susceptible to it when they sleep on their backs. Edison 22:04, 14 May 2007 (UTC)

Another factor affecting direction faced while sleeping (for me at least) is that I find breathing much easier when facing the room and the window than with my mouth facing the nearby walls. I have trouble sleeping straight, since most beds are slightly shorter than I am. But that's enough OR. Algebraist 00:11, 15 May 2007 (UTC)

Extreme p[H]s

Hi everyone - I was reading the superacid and superbase articles earlier in the week, which got me thinking: what is the highest pH measured thus far (and the lowest)? I appreciate that a lot of superacids may not be able to be accurately measured on the pH scale, so a rough approximation would do :) Thanks, Martinp23 21:38, 14 May 2007 (UTC)

Negative pH exists, see also this faq. this article tells us that magic acid has a pH of –25 (now added to superacid article). DMacks 22:59, 14 May 2007 (UTC)

Need help with definition: Atherosclerosis or arteriosclerosis?

Arteriosclerosis redirects to Atherosclerosis, but the article says that atherosclerosis is a specialised form of arteriosclerosis.

I'm trying to write a 'for dummies' definition of arteriosclerosis, but the article isn't helping. It keeps jumping back and forth between artho and arterio, and my head's starting to spin. Help please? Is arterio the main disease? Are they really that different? Anchoress 22:45, 14 May 2007 (UTC)

They are generally used essentially as synonyms, though there is a subtle shade of difference. Arteriosclerosis emphasises the hardening and thickening of the arterial walls, with accompanying loss of elasticity; atherosclerosis emphasizes the atheromatous (fatty) deposits that (usually) accompany the disease. - Nunh-huh 23:26, 14 May 2007 (UTC)

The arter form shall tell more to most people who already know about arteries. The ather one, otoh, is slightly more encyclopaedical. What should we have here in WP ? -- DLL ^{.. T} 18:55, 15 May 2007 (UTC)

Thanks very much Nunh-huh, for the clarification. Anchoress 18:28, 16 May 2007 (UTC)

Drugs that affect long-term memories

Hi my name is John and I have a hard time to answer one of the question of my homework.

- A drug can prevent long term storage of memories is ?

First of all I thaught about the kind drug like GHB or Rohypnol but I think that's more like a type of drug. Can somenone could help me out please ??

J.

Surely the textbook for your class contains the answer? --TotoBaggins 23:49, 14 May 2007 (UTC)

Hmmm. I would have thought that there's one extremely well-known drug whose ability to interfere with memory is notorious... --Robert Merkel 23:51, 14 May 2007 (UTC)

Me too, but I can't remember it since I started taking the Ambien. But more seriously, I'm not certain this is the answer, as it's most noted for short-term memory loss. - Nunh-huh 23:59, 14 May 2007 (UTC)

John, it's hard to say without knowing what you have been studying, because there are so many possible answers to the fill-in question. There are many drugs which interfere with memory formation, but it sounds like the question is asking for one which specifically interferes with short-term to long-term memory transfer (the "consolidation" phase of long-term memory formation), rather than by interfering with attention, or short-term memory formation, or memory retrieval. The benzodiazapines are one type of drug which does this, but there are others as well, so it's hard to say (unless you've just finished a chapter on benzodiazapines.....) - Nunh-huh 23:59, 14 May 2007 (UTC)

May 15

Can anyone identify this bird?

I took this picture of a dead hummingbird today. I know it's pretty low quality; but the number of hummingbird species that don't have images on Commons is staggering and I thought if anyone could identify it maybe it'd be useful someplace. So, does anyone know what kind of hummingbird this is? The picture was taken on the street in downtown Indianapolis. The bird is under a Honey locust tree. The nearest flowers are some Pansys in a pot on the corner. ~ ONUnicorn^{(Talk|Contribs)}problem solving 00:39, 15 May 2007 (UTC)

Realistically, I don't think there's any chance of a definite ID from that photo and it won't really be any use for illustrating articles. Maybe if you'd gone (much) closer with the camera... but at that level of detail it's not even very clear that it's a hummingbird. Sorry. --YFB ¿ 01:08, 15 May 2007 (UTC)

To add to that, for your own interest, a quick google suggests that it's likely to be a female Rufous hummingbird or Ruby-throated hummingbird, as they're the species with roughly this colouration most often found in Indiana. The female Rufous is near-enough indistinguishable from Allen's hummingbird, but there's no confirmed records of them in Indiana, although that could just mean nobody picked them out from the Rufouses. Cheers, --YFB ¿ 01:16, 15 May 2007 (UTC)

I'm pretty sure it wasn't a Ruby-throated hummingbird, and I don't think it was a Rufous hummingbird either. I've seen quite a few Ruby-throated, and even the females have more color then the dead bird in the photograph. Fewer Rufous visit my feeder, but I think the females of that species are sort of brown, aren't they? This one was pretty black-and-white, rather than drab brown. I know my keychain camera is shoddy, especially at close up, but while it looks like it could be blown highlights on the birds chest the feathers were white there. The bird caught my interest for a couple of reasons; first its location (no flowers around to speak of - and I hadn't seen hummingbirds downtown except by the canal and the state park), and second that I didn't recognize it as looking like hummingbirds that visit my feeders. Oh well. Thanks for trying. ~ ONUnicorn^{(Talk|Contribs)}problem solving 02:31, 15 May 2007 (UTC)

You may be right - I have zero hummingbird experience as I live in the UK. I've just had a look in my National Geographic Field Guide to the Birds of North America and I'm inclined to think it's an immature female ruby-throated. Based on location and markings, it's pretty unlikely to be anything else, as far as I can see. That would give it a whitish underside and throat, greenish-dark upperparts, probably less colour than an adult bird. Next time, try and get a closer photo! :-) --YFB ¿ 04:15, 15 May 2007 (UTC)

I hadn't thought about it maybe being imature... this time of year that's a good possibility. ~ ONUnicorn^{(Talk|Contribs)}problem solving 16:03, 15 May 2007 (UTC)

Can anyone explain me The mechanism by which sound wave propagates through air ?

interactive external links are welcome . —The preceding unsigned comment was added by 202.56.7.130 (talk) 01:52, 15 May 2007 (UTC).

Is our article on sound of interest? Splintercellguy 02:06, 15 May 2007 (UTC)

From looking at it, the article on sound isn't quite so helpful in explaining the propagation of the sound wave, but there's a bit of useful info in the article on longitudinal waves, of which sound is an example (and the external links look pretty handy, too). Confusing Manifestation 02:09, 15 May 2007 (UTC)

Sound waves are compression waves, they move through the air by quickly compressing and decompressing the surrounding molecules. Human ears are evolved to recognize certain frequencies of these compression waves as "sound". - 2-16 12:29, 16 May 2007 (UTC)

what is the aspect ratio of a normal human eye ??

Many computers monitors have a 4:3 but some, but some monitors have others, the aspect ratio of a cinema screen is not 4:3 is another one..... And the aspect ratio of your eyes what is what aspcect ration we see?? —The preceding unsigned comment was added by 201.8.100.1 (talk) 02:48, 15 May 2007 (UTC).

I don't think the concept of aspect ratio is applicable to the eye. Splintercellguy 03:07, 15 May 2007 (UTC)

Since the human visual field is circular, I suppose you could call the aspect ratio "1"; i.e. x = y. -- MarcoTolo 03:16, 15 May 2007 (UTC)

Conducting a little OR by staring at a wall and holding up my hands, it appears that, without moving my pupils, roughly 2/3 of the field of view of one eye is visible to the other. Head-mounted display says that the standard human interpupillary distance is 2.5-3", and visual field says that each eye can see -90° to +35°. I have seen standards for maximum recommended line length to make web pages comfortable, but I am not sure that that translates into any "most natural" aspect ratio. The fovea gives good detail and colour vision in the central 2° - taking a interpupillary distance of 7 mm and looking straight ahead, the fields of view of both fovea meet at a distance of one meter. Meaning that at that distance, the aspect ratio of your "good" vision will be 2:1 (as two tangent circles, not a rectangle), and closer in it would be two non-intersecting circles. Eldereft 04:40, 15 May 2007 (UTC)

OR: I measured the distance between the furvest points I can see to either side of, above and below my head, and it appears that my vision is an oval with a ratio of 8:3. but I expect this was distorted by the fact that I can see slightly backwards out of the very edges of my eyes. So I will see if I can find a better way to work this out.

I think I have worked out now that it is about 5:4, which seems a bit more likely. But in a way this is subjective. Maybe someone can work out an official test to see what shape we see.

The question has many answers, since the human visual system is very complex compared to a motion picture projection system, television display, or computer monitor. The human visual system includes in the retina a fovea, the area of most distinct vision, about 1 degree of visual field across, where cones, the receptors for color and for daytime vision, are most highly concentrated. This is smaller than the size of the thumb at arm's length and larger than the image of the moon. On a computer screen this is only a word or two wide at normal viewing distance. This foveal area of distinct vision is used to see by a sequence of largely automatic saccades or eyemovements, occurring several times a second, which are used to examine and analyze the visual environment. The area of distinct vision for a given fixation varies sightly between indivisuals, but is slightly wider horizontally than visually. Outside the area of distinct vision is an area which detects general shape and color and movement. [7] states that the binocular visual field (including less distinct vision) is 200 deg (w) x 135 deg (h), which sounds like an aspect ratio of 1.48. That source states that the area where the vision from the two eyes overlaps is 120 deg (w) x 135 deg (h), which would be an aspect ratio of 0.89 for actual stereoscopic vision. But in practice we look at something by moving the eyes in a sequence of saccades, and by moving the head when necessary, so the aspect ratio of vision is undefined. Edison 14:36, 15 May 2007 (UTC)

voltage

Suppose the reading on a voltmeter was "12 V". What would that mean, specifically? —The preceding unsigned comment was added by 68.20.221.168 (talk) 03:28, 15 May 2007 (UTC).

Well, it would mean that the potential difference between wherever the voltmeter probes have been placed is 12 volts. Also see the voltage article. -- MarcoTolo 03:48, 15 May 2007 (UTC)

There's also meter loading to consider (some current flows through the voltmeter), though it will probably be insignificant. If, for example, the impedance you place in shunt with the voltmeter probes is comparable to the internal resistance of the meter, connecting the meter will significantly alter the potential drop. The assumption that the meter reading accurately reflects the (unloaded) potential drop is valid if the internal resistance of the meter (typically a few megaohms) is much higher than the impedance over which the voltage is measured. -- mattb 01:22, 16 May 2007 (UTC)

Your car battery has a reasonable state of charge? But if you were measuring your mains electricity (wall voltage), it would mean it's time to call an electrician.

Atlant 14:11, 15 May 2007 (UTC)

Hmm. Just a warning that no one should attempt to measure their mians voltage without a proper safety voltmeter with fused leads and without proper training.

Energy from gravity

What would happen if you were far out in interstellar space tossing rocks trailing cable into the sun? Obviously the rock has (steadily increasing) velocity, so you should be able to capture mechanical energy from the cable and then let it "recharge" by allowing the sun to accelerate it again? A great distance from the sun the rock wouldn't accelerate much ("recharge" very rapidly) but eventually it would get close enough to produce considerable energy, right?

And of course, the obligatory black hole angle: what would happen if you were tossing rocks into a black hole? Would that be an infinite source of energy? It seems that if launching rocks into the sun would produce energy, it shouldn't be a problem if an event horizon is somewhere in between, as long as you don't expect to retrieve that rock..

I guess the question is: doesn't this violate the first law of thermodynamics? My guess is no, that you wouldn't be able to capture very much energy from the cable because fairly soon you're accelerated to the same speed as the rock. I suppose the more fundamental question is: where is this energy coming from that "enforces" the law of gravitation? Is it inherent in the mass? Does every combination of bodies in the observable universe have a potential energy to every other combination of bodies? And what about the uber-kilograms of mass that is revealed every second as the sphere of our observable universe expands at the speed of light? Shouldn't objects be wrenched out of orbit as black holes and quasars are "uncovered"? Or does our observable universe already have enough local mass to render insignificant any mass more than that distance away? --froth^t 04:26, 15 May 2007 (UTC)

How are you going to get usable energy out of this cable attached to the rock being pulled towards the sun? You'd have to be standing on something, otherwise the cable would pull you towards the sun too. Is that thing you're standing on also being pulled towards the sun? DMacks 04:35, 15 May 2007 (UTC)

Well presumably not as quickly as the rock, since the rock is much closer. But no you're not standing on anything, and that's why I suggested "you wouldn't be able to capture very much energy from the cable because fairly soon you're accelerated to the same speed as the rock". But obviously there is some energy to be had from the system of two bodies moving toward each other.. so where is that energy coming from? --froth^t 04:46, 15 May 2007 (UTC)

If you are on a planet then it's not a matter of simply throwing the rock, you have to launch it to escape your gravity first, which takes an enormous amount of energy, you will then probably spend the rest of the rock's trip to the sun recovering that energy. If the rock starts off in space, like a comet or something, then sure you could shoot a harpoon into it and then steal the energy from it, but since we have only just successfully landed the very 1st probe onto a comet, and the amount of energy and effort that required I doubt a rope with a generator on the end is going to recover even close to what was spent. Then the generator also would probably need to be shot back to earth somehow, using a lot more energy, or it would also just follow the rock into the sun. As to your question, yes I believe all mass has gravity as an inherent property and therefore there is potential energy between every mass in the universe, no matter how miniscule, it acts both ways, the earth exerts a gravitational force on the sun just as the sun does to the earth. Earth's effect on the sun isn't as noticeable, but Jupiter's effect on the sun is quite substantial, just as the moon's effect is very noticeable on earth. Vespine 06:03, 15 May 2007 (UTC)

One more thing for perspective, the point at which the gravity effect of the sun will outweigh the effect of the earth on your rock, only after which you can attempt to extract energy out of the rock without only getting back the energy you put in is called the L1 Lagrange point, about a million miles from earth. So your rope would need to be considerably longer then that, compare that to the circumference of earth is 25,000 miles, you can see another problem.. Vespine 06:12, 15 May 2007 (UTC)

Huh? You're not on a planet at all! --froth^t 06:39, 15 May 2007 (UTC)

All it does is shoot ya! 213.48.15.234 08:04, 15 May 2007 (UTC)

How about this for a contraption to get energy from gravity: Start with two asteroids which orbit one another at close range, tidally locked, in a highly elliptical orbit. Build a rigid connection between them with a sliding mechanism to adjust for the changing length between the two. This sliding mechanism will then be driven back and forth as they orbit one another. This motion can drive generators. Over time, this would change the orbit of the two asteroids, which would become more circular, I believe. StuRat 06:48, 15 May 2007 (UTC)

But wouold this produce more power than it took to make themechanism and find/get to the asteroids?

The Rance tidal power plant is a simply approach to the problem! Physchim62 (talk) 07:33, 15 May 2007 (UTC)

In any of these schemes, you are extracting mechanical energy from interactions between two or more bodies inside the gravitational potential field of the sun. This energy inevitably comes from a decrease in the total gravitational potential energy of those bodies - that is, their overall centre of mass must move closer to the sun as a result. The energy source is therefore not inexhaustible, although it's OK for a while. As Physchim points out, tidal power generators work on exactly this principle. Tidal power generation therefore leads inexorably to an increase in global warming!

Because of the inverse-distance law for gravitational potential, events in far-off galaxies fortunately don't affect us very much. --Prophys 08:57, 15 May 2007 (UTC)

AFAICT this is a question about how gravity works, but everyone seems to be sugesting ways to produce electicity from gravity :( The OP asks 'where is this energy coming from that "enforces" the law of gravitation? Is it inherent in the mass? Does every combination of bodies in the observable universe have a potential energy to every other combination of bodies?' :) Noone seems to have answered this, so I am asking it for them down here :] HS7 11:42, 15 May 2007 (UTC)

Asking how one gets energy "from" gravity is somewhat misguided. In a Newtonian universe, we can say that there is a gravitational potential throughout space, and that gravity is that variable energy (per mass); ${\vec {F}}:=-{\vec {\nabla }}U$, or "force" is simply the result of sitting on an energy gradient (you are accelerated down the gradient). Semi-classically, we can note that, just as a spring gains inertia from being compressed, so too does a mass gain inertia from being raised out of a gravity well (this is of course $E=mc^{2}$). Of course, we might then specify the rest mass of an object as its mass at infinite remove from all other masses; in practice, part of the rest mass of any real object is then "missing" because of its interaction with other mass.

So when you drop things toward a star (or whatever other convenient attractor), you are literally scavenging their mass energy for your own use (by letting the object represent some of its energy as kinetic energy, and then stealing that). If you drop them into a black hole, you do not recover infinite energy, but you can in theory recover their entire rest mass as they fall in (but note that this takes infinite time in any reference frame that does not fall in). This raises the interesting notion (although I cannot vouch for its literal correctness) that what mass is is one's gravitational potential energy as referenced against a handy Schwarzschild event horizon. In true general relativity, where gravity is not a force, this gets a bit more complicated: you are then taking advantage of a curved space to "circumvent" conservation of momentum: you have the object exert a force on you (and thus you a force on it) without accelerating it (although you are really accelerating the system of the star and the object). If one could in general get this "force without acceleration", simply tying a spring to a moving, unacceleratable object would allow you to get free energy forever.

As far as "new mass" in the universe, a simple explanation is that a (uniform, spherical) shell of mass exerts no gravitational influence whatsoever on objects within the shell. So the mass revealed by our expanding light cone, as long as it is at least approximately isotropic, has very little effect. --Tardis 15:47, 15 May 2007 (UTC)

Ah that last one's a good point, although I doubt it's anywhere near a constant increase in all directions since the speed of light is awfully slow and supermassive phenomena are so rare. Anyway, are you saying about black holes that since the rock has nowhere to go but down after passing the event horizon, you can capture as much energy from the cable as you want and the most that will happen is it will slow/stop until you let go again? Seems identical (though more efficient certainly) to using the gravity well of a star to do the same thing, although in that case you are able to recover the rock and it doesn't pull nearly as hard. But in either case, where's the energy coming from- is it only the rock's compromised potential energy within the system or does the very act of capturing the energy and accelerating along with the rock toward the star/singularity also contribute to the energy collected? --froth^t 18:05, 15 May 2007 (UTC)

1. About isotropy of the far universe: it has to be anisotropic in terms of the total distribution to have an effect; the individual blips are lost because of the inverse square law.

What about the Great Attractor? When that became causally connected to our universe, it must have caused quite a disturbance --froth^t 02:26, 16 May 2007 (UTC)

The Great Attractor's gravity at this distance is about $4\times 10^{-13}$ m/s², taking it to have $10^{4}$ Milky Way masses and the closest suggested distance of 150Mly. Next candidate? --Tardis 16:15, 16 May 2007 (UTC)

That number is impressively small, sure, but I've just realized a more fundamental answer: everything in the Milky Way experiences that tiny acceleration equally (remember that tides go as $r^{-3}$!), so it makes no difference in our local affairs. Moreover, we are always in free fall with respect to everything except the Earth, so a local experiment can't notice anything else's gravity anyway (and on this scale "local" is pretty big). --Tardis 16:23, 16 May 2007 (UTC)

1. About black holes: as I said, you can only get the mass energy of the rock. (For even a reasonably sized rock this is a lot, but it's not infinite.) All that happens is that, in your reference frame, the rock never stops falling (you never see it pass the event horizon, even), so you can keep running your pulley forever (but more and more weakly such that the total energy gained is, again, finite).
2. About the source of the energy: it's quite literally the potential energy the rock already had (and which already had inertia) before you started lowering it. In relativity "potential energy" is a particularly unfortunate choice of terminology because it is energy (and thus has inertia and gravity and such), not just some nebulous substance that might one day become real and start having an effect on the world. Gravity is simply a means of turning that kind of energy into the moving kind of energy — which still has inertia and gravity; this is "mass increase", although falling objects, until slowed down, are not changing in mass at all — and for distorting spacetime so that the falling object doesn't lose mass in its own frame. There really is no "source" for the energy; by dropping a stationary rock onto the surface of a planet, you are dropping a less massive rock than the corresponding rock that wasn't tied to a generator and landed hard, and you should not then be surprised that you have more energy on board your ship when you choose the former dropping strategy. The fact that the energy can be usefully extracted (we'd rather have a charged battery than an uncharged battery and a rock) is simply a result of the object's fall being reversible, which means that there is no entropy "bound up" with the energy released by the drop. --Tardis 23:04, 15 May 2007 (UTC)

Urgh - this is confusing. So you are in a spaceship - stationary relative to the sun and some large distance away. You have a large spool containing a few million miles of very thin cable - with the center of the spool attached to an electrical generator so you'll make electricity as the drum spools out cable. You tie the loose end of the cable to the rock - and toss it overboard. So to start with, the rock just floats slowly off into space at whatever speed you chucked it. But your spaceship is now falling towards the sun - you have to use your engines to stop it from falling. But now the rock is falling away from you...although it'll seem a lot like your engines are powering you away from it! However, your idea is that as the rock gets much closer to the sun than you are, the suns' gravitational field will increase and the rock will accellerate faster - eventually, producing more energy than your rocket is consuming to keep you hovering at the same distance from the sun. OK - that's probably a reasonable thought experiment. But what happens when the rock hits the sun (or melts or reaches the end of the cable or something)? At this point - you have no more energy income. All you can do is reel back the cable, tie another rock onto it and do it again. The trouble is that you don't have an infinite supply of rocks - because you have to use the power of your rocket engines to prevent both your ship and your supply of rocks from falling into the sun. So yes, you can extract energy from a falling body - but there is no free lunch here. It's no different from using a rope with a pulley and a rock on the end to generate energy here on earth. Your rocks have 'gravitational potential energy' by virtue of how far they are from the sun - when you drop them (attached to a cable), that turns into useful energy - but you've lost that gravitational potential energy - and the only way to get it back again is to haul the rock back up again - which takes more energy than you gained by dropping it. The fact that the gravitational field intensifies as you get closer to the source doesn't change that at all. If you change the experiment a bit and assume you are orbiting the sun instead of sitting still, you've saved the cost of keeping your engines running to stay in one place - but now the rock doesn't want to fall - it wants to stay in this nice zero g orbit. But if you pushed it out the door hard enough, and in the right direction (ie back along your orbit), the rock would start to fall into the sun and would unreel the cable - but you've still lost energy in the process because you don't have the gravitational potential energy of the rock anymore. If you are on a nice large planet instead of a spaceship - then you could certainly have an enormous supply of rocks - and powering your civilisation by launching large rocks into the sun with cables attached to them could theoretically work - but it's not "free" energy because the rocks you toss off of your planet don't come back. It might be a really cheap source of energy - and it might last you for a very long time - but it's not renewable - and it doesn't violate the laws of thermodynamics. SteveBaker 19:03, 15 May 2007 (UTC)

The worries about keeping your rock-dropping platform stationary are unneeded; just put your platform at some Lagrange point (between Earth and Sun, between Sol and Proxima Centauri, whereever) and you're set; then drop rocks a little ways away in equal amount in each direction and run two generators at once. The practical importance of this sort of technology would be taking rocks from reasonably high-potential areas (like the asteroid belt) and moving them (permanently) to a lower potential location like the Sun or a black hole; even the surface of Venus (where no one would mind the hail of rocks) would give you a specific energy of 54.7kJ/g, which is better than methane (not bad for "burning" a rock!). Obviously a black hole is the ultimate pit, and yields the full c² value of $8.9\times 10^{10}$kJ/g. No one's claiming that this is perpetual motion; indeed, I've tried to make it painfully clear that there is no "creation" of energy at all, even at some "expense" that would satisfy the first law. You're right, then, of course, that it's "non-renewable", but on the scale of civilization that we're talking about nothing is renewable, not even solar power! --Tardis 23:04, 15 May 2007 (UTC)

On a somewhat related note, I had a really weird dream last night. I dreamed that in the future, power was produced by "electrolysis towers". These towers were large columns with smaller pipes in the middle. Water would be produced by a hydrogen-oxygen fuel cells at the top of the columns, which would then flow down the pipe in the middle, generating hydroelectric power via generators as it traveled downward. The water was then electrolyzed into H2 and O2, which floated rapidly up to the top of the column due to the heavier gas (Think it might have been Xe or somthing in my dream, I forget. Lets call it UF6 just for kicks.) filling the columns. A high (90%) efficiency fuel cell (hey, come on now, its the future) converted the H2 and O2 into water, which then flowed down the column, starting the process over again.

Would this conceivably work, or would the columns have to be huge, 50 mi tall, and only make like 250W of power? Ninja! 23:44, 15 May 2007 (UTC)

No, I would expect the electrolysis of water to take more energy than you get back. StuRat 01:40, 16 May 2007 (UTC)

The solution is a Dyson sphere. - 2-16 12:31, 16 May 2007 (UTC)

StuRat, I realize that the electrolysis of water would use more energy (due to resistance and loss of energy to heat) than would be stored in the H₂, and that the fuel cell would also be somewhat inefficient, but, the idea is, that the energy of gravity uses hydroelectric power to create more energy than what is lost. Its really completely impractical, now that I think about it, but , as a thought experiment, you could either disprove the first law of thermodynamics, or.... prove that gravity is a continuous source of energy that is generated by the continuous loss of particle's mass to energy... O.o Ninja! 21:47, 16 May 2007 (UTC)

The failure of this device is that it takes energy to force the heavy gas aside at the bottom of the column (PdV and all that). That energy is what you're attempting to tap by having the falling water run a turbine. --Tardis 23:15, 16 May 2007 (UTC)

Antidepressants

What do they do to the mind? Chemical effects to the brain are I assume widely understood, but can anyone who's taken them tell me what they actually do to you? Does it just improve the disposition of the person or what? I certainly understand feeling good and readily laughing, etc, and also being depressed and inexplicably moody.. but do the drugs actually do anything besides affecting that aspect? Seems hard to believe that a person's reactions and general smileyness could be affected by something as insignificant as disposition instead of deeper-seated things like personal philosophy --froth^t 04:44, 15 May 2007 (UTC)

It varies. When I took Paxil (1994), my mother and my ex-wife both commented that I was more willing to approach people; that's the most striking effect I remember. Later I took Prozac and Wellbutrin, with mixed results; at best, they simply relieved me of the occasional attacks of despair. When I stopped taking Wellbutrin (because of palpitations) my mood actually improved for a few weeks. —Tamfang 05:18, 15 May 2007 (UTC)

Basically, they raise the level of serotonin and other neurotransmitters in the brain. I tend to think of hereditary depression as the diabetes of the mind. It hits a lot of males at 40 and gets progressively worse. People tend to self-medicate with alcohol and drugs. The anti-depressants are a better alternative than addiction and suicide, but they do tend to level things out, and reduce creative spurts. --Zeizmic 11:30, 15 May 2007 (UTC)

I think the most common kind now is SSRI's (Selective seritonin reuptake inhibitors), which reduce the rate at which Seritonin is removed from the brain, thereby increasing overall levels. I had a kind of messed up childhood up until about age 12, and was on SSRI's for about 2 years (age 10-12)- I assure you, not by choice. I never really understood this, as I never really felt depressed in the first place, I think it was mostly to due my percieved "behavioral disorder" which now seems to be more of a PG/ADHD-BD misdiagnosis (Huh, no article about that, think I might write one). But anyway, more to the point, most of my friends told me that it did improve my mood and disposition somewhat, at the expense of a loss of personality and creativity, it kind of mellowed me out. Oddly enough, I actually felt better for a time after I stopped taking the medicine, though perhaps I am a bad example as my doctor (but unfortunately still not my mother and the morons on my district's school board, but thats not the point) both agree that I was misdiagnosed. Hope I spent more time helping than I did whining about grades 5-7 :/ Ninja! 23:57, 15 May 2007 (UTC)

Oh, on another note, I think some of the newer antidepressants also work by affecting noropinepherine (oh boy, I misspelled that, I'm certain...) Ninja! 00:06, 16 May 2007 (UTC)

It's norepinephrine, also called noradrenaline. Icek 12:35, 16 May 2007 (UTC)

When I was younger, I was diagnosed with ADHD and Bipolar disorder, because it was the late 90s, and it was cool to be a kid on ritalin. I was given Ritalin and Depakote. I don't remember exactly what it was for, but I'm fairly sure that the Ritalin was to calm me down, and the Depakote to cheer me up, although oddly enough, my mother had taken depakote a couple decades earlier for her seizures. Anyway, I don't remember it very clearly, but I do remember that while I was on them (both of them), it actually made me more violent and angry. I "forgot" to take my pills one week, and was much more well behaved, and in general, normal. I know that once I quit taking them, I improved quite a bit. One side effect I definitely remember was weight gain, due to an incredibly unprofessional shrink. Still haven't fully gotten over that. I don't know if there's any medical proof behind it, but I firmly believe that one of the three drugs (Ritalin, Depakote, and Neurontin), or a combination of them, messed my memory up extremely badly, as I have very little memory of even huge things from then, and my memory still suffers some, mainly short term, although it's improving. I'll have memories I should have missing, like I can remember a name, but even when I'm given very detailed descriptions of people and how they act, I can't remember 'who' they are, or I can remember 'who' someone is, but their name is completely lost on me, and I'm not talking about random people here. Hell, up to a couple years ago, I had trouble remembering faces of even close family and friends, I still have times when I can't even remember what my own mother looks like. Obviously chemicals can have a very real effect on how people act or feel, look at narcotics, booze, any number of things. I still recommend against them though, if I had to go through it again, knowing what I know now, I'd much rather go to therapy three times a week than put that stuff back in my blood stream -- Phoeba Wright^OBJECTION! 02:35, 17 May 2007 (UTC)

electron and proton attract each other then why there are distance between them in an atom ?

consider a hydrogen atom which is simply made of a n electron and a proton ; but there are distance between these two . why these electron and proton do not simply touch each other to form an atom ? —The preceding unsigned comment was added by 202.56.7.134 (talk) 09:09, 15 May 2007 (UTC).

1. They're an atom without touching each other. Electrons and protons don't touch, and we still have atoms. Plenty of them in fact. Did you mean nucleus?

2. "Touch each other" doesnt really happen at atomic scales. The electromagnetic fields interact.

3. The Earth and the Sun are in a nearly identical situation, they are attracted by gravity. Why don't they touch each other to form the death of humanity^TM?

Have you studied Centripetal force?

(I know i'm using a Bohr model here, anyone care to explain it with QM?). Capuchin 09:16, 15 May 2007 (UTC)

Yeah it's certainly not centripetal force! The electron doesn't sit in one place in space, it really lives in a sort of probability cloud all around the atom. It's hard to picture, but effectively the electron can be found anywhere within this area around the nucleus, including 'touching' the proton, but is simply more likely to be found a slight distance from the nucleus. It's all a bit quantum. I am sure the article on hydrogen atom would help. 137.138.46.155 11:33, 15 May 2007 (UTC)

Also atomic orbital. DMacks 14:50, 15 May 2007 (UTC)

Unfortunately, none of the above seems to really answer the root question (which I'm reading as "protons are positive, and electrons are negative. Since opposites attract, why don't they smash together?" -- correct me if I'm wrong). It's an excellent question, and unfortunately doesn't have a simple answer. The best I've come up with is to reference quantum electrodynamics, which notes that at very small (i.e. atomic) scales, electromagnetic forces aren't really doing what we think they're doing at macro scales. That is, at their smallest most fundamental level, opposites don't attract. Rather, they swap mediating particles (in this case, virtual photons) that affect the nature of the originally exchanging particles.

So, as best I read all this, a proton and an electron aren't really attracted to each other. Rather, they bounce these virtual photons back and forth, which leads to the behavior described in the above referenced articles like atomic orbitals. By the time you get up to large scales, the sum total of the behavior is such that opposite charges, for all intents and purposes, do attract. It's weird, yes. And I don't know why virtual photons make electrons do the things they do. However, that appears to be the core of the answer. — Lomn 15:49, 15 May 2007 (UTC)

Two interesting issues come to mind here:

Sometimes something approximating the macroscale concept of "an electron colliding with a proton and sticking" does occur (electron capture decay).

One fundamental thing that's really hard to understand at all, let alone remember and see all the resulting effects, is that electrons are not really point particles. They can do all sorts of things that a macroscale object cannot, and they don't have definite positions and motion around the nucleus.

Even in atoms, the idea of electrostatic attraction is a good model for lots of behaviors (for example, decreasing atomic radius going across each row on the periodic table), but it's not the complete picture.DMacks 17:23, 15 May 2007 (UTC)

Electrons "orbit" like planets around the nucleus (protons + neutrons) of the atom. These electrons must orbit at a certain speed. If they went any faster, they'd escape into space (or move into a wider orbit). Any slower and they'd crash into the nucleus (or move into a smaller orbit). So faster electrons orbit farther from the nucleus.

To change speeds - and so change their height - they'd need to change their energy. This is not possible (due to conservation of energy) unless some additional force comes into the system. For example, a photon with enough energy can knock an electron completely out of orbit (this is ionization).

This explanation mirrors the Bohr Model, and is false but a good approximation. A better model uses quantum mechanics and modifies the picture in 2 ways. (1) The atoms no longer orbit, but are sort of fuzzily spread out (delocalized) along the entire path of the orbit, so the electron as a single point becomes an fuzzy circle or sphere. (2) It allows only certain heights (and paths) above the nucleus to be valid orbits (see atomic orbitals).

Electrons will try to get into the innermost orbit (remember, QM says only certain orbits are allowed). Electrons can move into smaller orbits if there's not an electron in that orbit already (Pauli's exclusion principle). To move into a smaller orbit, they need to have less energy, so they convert the excess energy into a photon and emit it.

To answer why the electron doesn't lose all it's energy and crash into the nucleus, I guess it falls out of QM, but don't ask me how. I guess that if it did happen, it would interact with one of the protons, and make a neutron (β+ decay). But this would require extra energy, so would not be possible.

This is really a brief overview, and a hand-wavey description, with many generalizations and omissions. Bohr Model is a good place to read more; the Standard Model is the currently accepted model. --h2g2bob (talk) 17:25, 15 May 2007 (UTC)

There are many answers to that question. Oni is that, on an atomic scale, electrons don't act like little balls or points but wavelike and thus don't have a pointlike coordinate position but an expectation desnsity.

A quite different answer is that if they fell into the nucleus and reacted with a proton to form a neutron, that would require additional energy, as a neutron is slightly heavier than the mass of a proton plus the mass of an electron. 84.160.233.3 19:12, 15 May 2007 (UTC)

of course all this could just be pseudoscience, and there might actually be a totally different reason that we haven't discovered yet.

final starch question

forget all my previous questions about starch (to which I didn't get answers). I just need to know a quantitative test for stach. Something I can do to something with starch in to see how much there is. Say I have a leaf grown in darkness somewhere and I want to see how quickly stach in it is replaced, I would need to do something to the leaf occasionally to see how much starch had been produced. How would I do this? Or you could refer me to another websight which can tell me if you prefer. —The preceding unsigned comment was added by 172.142.244.7 (talk) 11:33, 15 May 2007 (UTC).

Seeing you display such a stack of insite, I'd like to help. "quantitative test for starch" in a Mountain View search engine returns 979 000 answers. Some just use spectrometers and amylase. So this is my question : what kinda devices and products may you use easily in your job (or homework) ? -- DLL ^{.. T} 18:49, 15 May 2007 (UTC)

Not spectrometers. I am quite sure of that. I was hopeing there were chemicals that can change colour, or something. I have already tried searching the web, and didn't find anything apart from a few pages vaguely similar to my question. I am apparently not very good at getting computer stuff to work.

Well, the classic Iodine-KI reagent test will reveal the presence of starch - but not the quantity. I suppose you could somehow use a very dilute version of the starch and match the resulting colour to some kind of a colour chart. You could calibrate the chart with known quantities of starch in increasingly dilute amounts. It wouldn't be really exact - but maybe good enough for your test. SteveBaker 17:08, 16 May 2007 (UTC)

Hospitals

How many hospitals are there in the United States?170.232.128.10 14:31, 15 May 2007 (UTC)

As of 2005, 7,569. Hipocrite - «Talk» 14:42, 15 May 2007 (UTC)

That impresses me as a small number. --BenBurch 14:52, 15 May 2007 (UTC)

Average of 150 per state is small? I guess it's all about lies, damn lies, statistics, and one's frame of reference:) DMacks 15:00, 15 May 2007 (UTC)

According to the OECD, in 2003 the US had 2.8 acute care hospital beds per capita thousand, vs 4.1 for all OECD countries.[8] Thus, we are below the developed country average in beds-per-capita. Hipocrite - «Talk» 15:06, 15 May 2007 (UTC)

Hope you don't mind me editing your remark, but 3 beds per person would be a trifle excessive, I feel. Given the US spends $5,635 per capita per year on healthcare, more than twice the OECD average, I hope they're very comfy beds. Algebraist 15:26, 15 May 2007 (UTC)

A quick note: that's 2.8 beds per 1000, not per capita. Otherwise you'll be left wondering why anyone would care if a patient has a fourth bed or not (or why it matters). There's also the question of how the metrics should be applied. For example, this MSNBC article notes that the US is generally good with regard to timely access to major surgery and preventative care. Perhaps that affects the need for hospital beds per capita (or maybe it doesn't, or maybe it puts the US further in the hole). Point is, statistics in isolation can provide a dangerously unwarranted level of confidence. — Lomn 15:30, 15 May 2007 (UTC)

Thank you both for the correction - yes, it is, obviously, beds per thou. Hipocrite - «Talk» 15:38, 15 May 2007 (UTC)

Absolute Uncertainty of a mean

If you have a set of data, knowing the absolute error of each object in that data (e.g. 20±1cm), and then find the mean of that data, what is the absolute error of the mean, assuming all of the elements of the data had the same absolute error?

e.g.

18±1 17±1 15±1 14±1

The question is phrased as find the mean (obviously 16) and then the absolute uncertainty of this mean.

The mark scheme from the paper I am looking at is talking about finding 1/2 or 1/5 of the range, or 1/2 or 1/5 of the range ignoring the highest and lowest answers.

Can you please explain the methods for finding these means? Or point me in the direction of where to look?

Many thanks!

--Fadders 15:30, 15 May 2007 (UTC)

See propagation of uncertainty, although you should be careful about whether you are claiming by $z=x\pm y$ that "z is certainly on $[x-y,x+y]$, but may be anywhere in that interval" or that "z is probably at a remove from x no greater than y, but will often be significantly closer or somewhat farther away" or any other such formulation. (In the second case it is commonly assumed that z is normally distributed.) The values you are reporting are really probability distributions (in some interpretations), so you need to give them a shape (presumably described by your "error" value) before combining them.

In the likely-correct interpretation as a normal distribution with a standard deviation as the error, you should look at that page and at, say, the variance of a sum to find a rule for the mean of your data. --Tardis 16:07, 15 May 2007 (UTC)

Hmm I'm not sure that's what I'm after.

The question is at http://www.aqa.org.uk/qual/gceasa/qp-ms/AQA-PHB3-W-QP-JAN05.PDF (page 3)

The mark scheme has the answer at http://www.aqa.org.uk/qual/gceasa/qp-ms/AQA-PHB3-W-QP-JAN05.PDF (page 4)

Thanks! --86.156.40.31 18

40, 15 May 2007 (UTC)

hydroponics

I recently read that some grow hydrponics by filling a ditch (in the ground) with water, and then having some sort of pipe with water which is connected to the water in the ditch- in this "pipe" grow hydroponics.

What is the purpose of this way?

do the hydroponics draw any nutrition from the soil by way of the water?

Thanks for your help

Tirzah Segal

email removed to protect you from spammers —The preceding unsigned comment was added by 86.135.202.234 (talk) 16:31, 15 May 2007 (UTC).

Chemistry (In general)

Is the only way to understand Chemistry (other than constantly solving extremely complex mathematics via approximations) just knowing how each chemical element reacts ? Sure, for the first two rows of the periodic table, most of the elements are well behaved with respect to the duet-octet rule and many bonds can be understood with solely this rule. Of course some subtleties arise with considerations of electronegativity and ionization energies, but it doesn't really get too unpredictable (even though some molecules seem to be quite different (Al₂Cl₆)). But then it seems on the lower rows, no real predictions are made, just observations. Why is it so often Mg²⁺ ? Why can Mn be reducted to +7 and not Fe to +8 ? Why is Hg liquid at normal temperatures ? Even the predictions based on comparing between rows aren't always very true, and other oddities like Zn reacting to HCl and not Cu. Surely there are precise explanations of how one can expect species to react ? I understand most imaginable (but not absurd) molecules can exist, and then one has to evaluate how stable they are. But still, what are the best rules that suit all ? I just get confused with the different treatments for different elements (Transition metals, semi metals, non metals, etc...), even though it is understandable differences must exist. As it is now, I'm totally unable to say if such or such molecule is stable (a book I'm reading always comes up with new explanations each time of why such molecule is stable : one time it's with atomic orbitals and combinations, one time with hybridization, one time with redox principles, ...). Are all the elements so different that one has to differentiate them clearly to be able to study their behaviour ? And even so, how does it work, what makes it possible to not study individually all elements in most cases ? --Xedi 18:43, 15 May 2007 (UTC)

Chemical properties of hydrogen compounds can have vast differences depending on the state of matter (solid, liquid or gas). The difference in chemical properties is related to:

a. the dissociation of H+ from the hydrogen compound into solution.

b. the dissociation of OH- from the hydrogen compound into solution.

c. the energy threshold required to break the covalent bonds in the solid.

d. the slight cohesion of the liquid solvent forming the aqueous solution.

—The preceding unsigned comment was added by 72.64.128.23 (talk) 18:46, 15 May 2007 (UTC).

Well, yes, but that stays a quite basic description. I do understand how Brönsted acids/bases work in water, but that's just one infinitesimal part of chemistry. I quite like how the K_A/pK_A system works, as one can just write down a reaction and see how it evolves, just knowing the K_A/pK_A of some species. But this still depends on "knowing" how the molecules react (ie knowing their K_A/pK_A). For more general reactions, there isn't even this, and it seems difficult to predict how atoms will combine, without just knowing how they react from observation. --Xedi 19:22, 15 May 2007 (UTC)

"Physics is the study of how things behave similarly. Chemistry is the study of how things behave differently" - George Pimentel. Delmlsfan 19:43, 15 May 2007 (UTC)

Haha, well, quite true. Sadly physics are too complicated (mathematically) here. Oh well. --Xedi 19:47, 15 May 2007 (UTC)

Well, a couple things on this one.

• Mg is reduced to a 2+ ion because that allows it to have an ideal electron configuration, eg., eight electrons in its valence shell (2S and 6P)
• Mn and Fe don't reduce to +7 and +8; this is not ideal for them. Transition metals often prefer to either shed all of their D orbital electrons or about half of them, as these are both fairly stable; still other transition metals prefer to do only 2+. Except for Ag+; and I beleive Hg has a 1+ state as well, though I think its diatomic or something weird like that, I forget about that stuff, I do organic. Anyway, back to the point:

Mn does have a +7 oxidation state. And you're right that the Hg +1 state is diatomic; it's Hg₂²⁺. See Mercury(I) chloride as one example. Chuck 23:28, 15 May 2007 (UTC)

I suppose I hadn't thought of MnO₄^-. I was thinking more of just an Mn⁺⁷ ion floating around in solution, which of course wouldn't happen. Ninja! 21:28, 16 May 2007 (UTC)

• As far as Zn reacting with HCl, Zn is more reactive than Cu. There should be an explanation for this at Reactivity series (if there isn't let me know, I'd need to edit that article some)
• As far as what molucules can exist and what can't- this is a very broad area. I'd check out the article on Lewis structure for this one; they can be helpful for predicting if a certain species exists.
• I think I forgot to mention Hg being a liquid. This is due to Intermolecular forces, especially Metallic bonding. I would check out the article on Mercury for this one.

I think that answers most parts of your question. If you have questions about a specific element, I'm sure the article about that element would be quite helpful; if you have some question about something more specific feel free to drop me a message on my talk page; I'd be happy to help. Ninja! 23:06, 15 May 2007 (UTC)

Hi,

Sorry about the Mg²⁺ one, yes that one is quite simple. I actually meant Mn²⁺. So why do so many transition metals reduce to 2+ ?

That [Reactivity series]] is very interesting and shows well the differences in reactivity. But still, why would Zn be so much more reactive than Cu ? I mean, Cu and Zn are nearly the same, only that has both s and d full (and Cu's electron configuration also doesn't fit in with the general trend of filling s first : [Ar]4s¹3d¹⁰ (same for Cr I suppose) : this conforms to your explanation of prefering to half-fill or entirely fill the d orbital, same goes for Ag and Au underneath Cu that also don't react much). This seems to be another example of how chemistry works : we get tables of what reacts in general with what, as in that reactivity series or with redox potentials. But for some elements it seems really strange to me. I feel quite confident I could come up with many more questions and that finally it would be as if there was an explanation for nearly every element (Tc being unstable, B being strange, ...).

Thanks for the explanations still. Just that so many things seem strange to me.

http://img518.imageshack.us/img518/1899/ptinorganicxf4.gif

-Xedi 11:42, 16 May 2007 (UTC)

Dark matter

Most mass in the univers is in the form of dark matter, how is it that we don't see even the gravitational effects? With huge additional quantities of mass around, planetary orbits should be different, stars should collaps at a different rate, and, finally, black holes should grow at a different rate. (Even the 'darkest' matter should not be able to escape again.) 84.160.233.3 19:18, 15 May 2007 (UTC)

We do see the gravitational effects - that's how we know that what we can see doesn't tally with the mass that is measured to be there. →Ollie (talk • contribs) 19:25, 15 May 2007 (UTC)

As far as I know we see only effects about gravitational lensing. There should be other, more direct effects. 84.160.233.3 19:50, 15 May 2007 (UTC)

We see that the orbits of stars around their galaxies are not as either Newtonian mechanics or general relativity (quite similar predictions at those scales) would have us believe. The only possible explanations to this is that we are very very wrong about how much stars weigh, our theories of gravity break down at huge distances, or there is mass that we can't see (it is "dark"). Most astronomers agree (I actually don't know of any who don't, I'm sure dark matter is a good read for this) that the third possibility is the correct one. Someguy1221 19:57, 15 May 2007 (UTC)

We see no effects on planetary orbits in the solar system. The dark matter is probably just elswhere in the galaxy or spread very evenly around. However, see Pioneer anomaly for another possible gravitational effect of dark matter. —The preceding unsigned comment was added by 84.187.9.82 (talk) 20:16, 15 May 2007 (UTC).

Now that I look at it, Dark matter is a very good read on this issue. And dark matter is everywhere, dude. Someguy1221 22:29, 15 May 2007 (UTC)

Yea, it's a good read and the article can't be blamed if science can't do better as of now. Anyway, if dark matter isn't very hot (fast), it should gravitationally agregate insides big stars and significally influence the point of gravitational collapse. Even if it were extremely fast, it would be cought by black holes from where it is no escape. Black holes would grow much faster then. This effect should be detectable. Why isn't it? 84.160.233.3 00:59, 16 May 2007 (UTC)

How do you know this effect should be detectable, have you calculated the effect? We can barely detect black holes as it is (because they are black!) and rely on seeing their gravitational effects, we certainly haven't been observing them over a long enough time scale to see how they grow. Why Dark matter is spread evenly rather than following the patterns normal matter has collapsed into is unknown. But then we do not know really what makes Dark matter up at all, only that it's gravitational effects are detectable. There are three main ways we see this, Gravitational lensing, rotation curves (i.e. speed of rotation of matter in galaxies and galactic clusters) and through projects like WMAP which fit all the observables we have to the development of the universe as a whole. From this they deduce how much ordinary matter, dark matter, dark energy etc must be in the universe to make it how it is today. I guess the answer to the question is that dark matter tends to have large scale rather than small scale effects. And we'll get back to you when we know what it is, the LHC particle accelerator switching on 2008 could very likely see some particles which are dark matter candidates, so watch this space. Cyta 11:56, 16 May 2007 (UTC)

The answer is obvious. All ninjas are made entirely of dark matter. Since the dark matter is contained within ninjas, we can never detect it. Because ninjas are awesome. - 2-16 12:34, 16 May 2007 (UTC)

Lead-acid batteries

Do lead-acid batteries of the type used in UPS systems, power wheelchairs, etc ship charged or discharged? Also, is it normal for a lead-acid battery to make a fizzing sound when charging? 65.188.253.13 19:23, 15 May 2007 (UTC)

Read Lead-acid battery. I learned a lot reading it. They are always kept charged, and that's why my friend had a bum battery when he bought a show car; they have to charge every 2 weeks. Back to your problem: if it fizzes and inflates like a balloon, that's not a good thing! Since this answer is a bit late, let us know if you survived the explosion. --Zeizmic 21:50, 15 May 2007 (UTC)

A lead-acid battery only fizzes when it's fully charged and breaking down water via electrolysis. It's not a normal condition but if you have a long string of batteries in series, it might happen when you're first charging the string and the batteries are "equalizing"; that is, they may have initially been charged to different points and the batteries that reach full charge first begin to "boil". Assuming these batteries use ordinary unsealed cells, then after that first charge, just top off all of the cells in all of the batteries with distilled water. But if they keep fizzing after that first full charge, then something may be wrong.

Atlant 22:58, 15 May 2007 (UTC)

Sealed or valve-regulated lead-acid batteries used in many DC power applications are stored and shipped fully charged, and can hold a reasonable charge for over 3 months. Past 6 months, and breakdown can happen as the battery flat-lines and starts to chemically deteriorate. If your battery is fizzing and it's a sealed or valve-regulated (meaning nonspillable) then it is deteriorating and I would not trust it to work for very long. These types are not fillable so as they burn off water there is no way to put it back! --Jmeden2000 18:25, 16 May 2007 (UTC)

Exercising and Sweaters

Does wearing a sweater help get rid of fat or calories during exercise? Or does it just get rid of water weight? PitchBlack 19:40, 15 May 2007 (UTC)

Exercise that requires more energy uses more calories, because the calorie is a measure of energy. So what you are really asking is, "Does wearing a sweater during exercise make you work harder?" And the answer is: yes, but not much. Wearing a sweater requires you to work harder, since a sweater has weight; you must carry it around with you as you exercise, and that takes some additional work. But not much, since a typical sweater is not very heavy. And the same effect could be achieved by holding the sweater in your hand as you exercise. --Tugbug 22:18, 15 May 2007 (UTC)

It would make you sweat more, which requires slightly more work I suppose, but you're likely to become tired more quickly than just exercising without a sweater, which is obviously preferrable. --froth^t 22:27, 15 May 2007 (UTC)

Well, it's not going to "burn" or "melt" any fat off. The best way to lose weight through exercise is to actually exercise and not give up on it, which will be considerably easier if it's somewhat pleasant to do, which will be considerably more likely if you're not doing it in a sweater. --TotoBaggins 17:52, 18 May 2007 (UTC)

How many HP do humans have?

So, how many?217.95.9.251 20:27, 15 May 2007 (UTC)

Over nine thousand. --Xedi 20:31, 15 May 2007 (UTC)

There's an answer, surprisingly enough, on the horsepower page. DMacks 20:34, 15 May 2007 (UTC)

Geez DMacks, you could have made it easier. I finally found it: "a healthy human can produce about 1.2 hp briefly...and sustain about 0.1 hp indefinitely, and trained athletes can manage up to about 0.3 horsepower for a period of several hours." Clarityfiend 20:40, 15 May 2007 (UTC)

How many 'homepages' do humans have? What, each? Or collectively? --Manga 20:47, 15 May 2007 (UTC)

It changes with each level depending on your constitution. --Russoc4 20:58, 15 May 2007 (UTC)

Defense is more important anyway --froth^t 22:25, 15 May 2007 (UTC)

I thought Hit points when I first read this, haha. :) Vespine 22:30, 15 May 2007 (UTC)

Umm...doesn't it mean hit points? bibliomaniac15 00:19, 16 May 2007 (UTC)

I thought it was talking about Hewlett-Packard, although the article doesn't give an idea of the total number of HP products owned by people around the world. Then again, it could be anything on HP (disambiguation), in which case I would point out that humans have one hippocampus each. Confusing Manifestation 00:46, 16 May 2007 (UTC)

Whatever they are, they taste very good when liberally coated with HP Sauce. (That's small l liberal, btw; not wanting to offend any British parliamentarians out there.) -- JackofOz 00:53, 16 May 2007 (UTC)

You just need to balance your food recommendations to insult all POVs equally, might I suggest a nice chicken catch-a-Tory ? StuRat 01:22, 16 May 2007 (UTC)

Well, a human's HP depends on their STR and CON values, of course. And their level.

If we seriously consider the question of how many hit points a person has, we need to acknowledge that it's a flawed question in the first place. Different gaming systems have different amounts of hit points. In Fire Emblem, 60 is the absolute maximum, whereas in Pokemon, 60 hit points is incredibly weak, with the maximum being well over 300. The only way in which we can derive a "universal hit point scale" is to find the average endurance of a human being and convert it to a numerical value. Of course, many factors need to be considered in this ("endurance" is rather vague); Body fat? Stamina of running? Bench press? Even if we can find the average human's endurance, what scale will that be on? Will an average human have 100 hit points, where 50 HP would be one half, or will an average human have 10 hit points, where 5 HP would be half? Reexamine the question, methinks. - 2-16 12:39, 16 May 2007 (UTC)

resistance of copper to strong alkali

To cool or heat a 10L tank of liquid quickly I am considering immersing a coil of copper tubing in the liquid and running hot or cold water through it. The problem is, the liquid in the tank is pH 12 (fairly alkaline); I am wondering if the alkaline will cause a lot of copper to go into solution. I am not actually worried about mechanical failure of the tubing, I just would prefer not to add a bunch of copper to my solution.

Any ideas on how to find out effect of alkali on copper? Alternatively, can you suggest a coating for the tubing that wouldn't be too bad of an insulator? Or do you have other ideas for a small scale heat exchanger? ike9898 20:52, 15 May 2007 (UTC)

I'm Not sure about the reactivity of copper with a base, but alternatives would be: cool or heat the tank directly, use a metal less reactive than copper, or find out what the inside of the tank is made of and use that material. --Russoc4 21:01, 15 May 2007 (UTC)

The tank is glass. I have considered getting a pyrex coil made, but it wouldn't be as cheap and easy as the copper. I'm also interested in other methods for benchtop heat exchanging. I can spend a little money if I need to, say $1000. ike9898 21:06, 15 May 2007 (UTC)

I don't believe any significant reaction will occur between Cu and OH- (That is, alkali conditions). Cu(OH)2 (Copper Hydroxide) Isn't formed spontaneously by reaction of Cu with a base that I know of, as you have to put energy in via, for example, electrolysis. I'm fairly certain that the copper will hold up fine in this environment. Ninja! 23:29, 15 May 2007 (UTC)

Dark patch on hand

On my right hand, where my thumb is connected to the hand, there is a patch of skin quite a bit darker than the surrounding area. When I put my thumb against my hand, this dark area ison the right hand side of the "crease", and is about 2 pencil-top erasers wide. It goes up along the side for about 4-5 pencil widths. I am a white male, 15 years old, and have had adbominal problems in the past few months, and have had moles throughout my life (some removed). Is this something I should worry about? 22:46, 15 May 2007 (UTC)

According to the top of this page, "Do not request medical or legal advice. Ask a doctor or lawyer instead." Although you might get some good information about this from Wikipedia, if you're concerned it would be best to see a doctor instead. Ninja! 23:31, 15 May 2007 (UTC)

Agreed, see a doctor. Some moles can become cancer, so it is important to have a dermatologist check them regularly, especially if they change in size, color, or texture; or if they become painful or itchy. Moles with an irregular boundary are more likely to become cancer, so especially see a doc if you have those. StuRat 01:11, 16 May 2007 (UTC)

Definitely see a doctor, who might mention the ABCD guideline. --TotoBaggins 18:06, 18 May 2007 (UTC)

biology

what are the common characteristics between animals and all living things? —The preceding unsigned comment was added by 144.120.8.37 (talk) 23:50, 15 May 2007 (UTC).

They all like to avoid doing their own homework ? StuRat 23:32, 16 May 2007 (UTC)

Try a google search, there is a lot out there. David D. (Talk) 03:53, 16 May 2007 (UTC)

DNA - although viruses don't have it - it's debatable whether we should call them "living things". Cell structures are present in everything other than viruses - so probably there are a range of structures within the cell that are common to most life-forms. If you are talking about things other than physical structures, we have: Reproduction, Nutrition, Growth, Excretion, Respiration. SteveBaker 11:39, 16 May 2007 (UTC)

The ten unifying themes of life (if I recall correctly) are evolution, homeostasis, reproduction, movement, adaptation, reproduction, and a few others which I can't be arsed to dig up right now. - 2-16 12:41, 16 May 2007 (UTC)

The fundamental (basic) unit of life is the biological cell; although even some viruses (such as papillomavirus, which causes warts) have DNA, they are not cellular and require a host cell to replicate, so are not regarded as "alive". Bendž

|Ť 13:39, 16 May 2007 (UTC)

life. and death. but not taxes.

mouse

I have a mouse that has been living in my gorage that i want to catch for a pet ive been seting traps but its goten away with the food from all the traps with out seting them off. So far the only times that the mouse has goten the food from the traps was dering the day when im at school and at night when im sleeping. Is there a way i can find out if it is just taking care of babeys without takeing every thing out of my gorage. Because i dont want to trap it if it is taking care of young. thanks --Sivad4991 23:55, 15 May 2007 (UTC)

Catching a wild animal for a pet is often a bad idea. For one thing the animal is likely to be infested with a variety of parasites. You are better off getting a pet mouse from a pet store. The mouse itself will be quite inexpensive compared to the cost of the cage etc. that you will need for it. 169.230.94.28 00:04, 16 May 2007 (UTC)

I'm assuming you want to get the mouse out of your garage, but want to be humane about it, and keeping it for a pet was your idea of how to do that. Another suggestion is to catch it humanely, take it out into the woods, and release it, then get a disease-free mouse from a pet store to keep as a pet, if you want, as suggested above. There are special traps designed to trap mice but not harm them. As for the mouse having babies, you don't even know if it's female, so I think it's unlikely it has babies. Also, you probably have many mice, not just one. StuRat 01:04, 16 May 2007 (UTC)

Don't trap the mouse. Wild animals do not like to be contained. I have a garden with many fruits and vegetables, and squirrels have taken note of it. Now, I don't mind sharing the fruits of my labor (no pun intended) with a fellow animal, but the darned things just take a bite and leave the rest to rot! After a few months, I got tired and decided to get a squirrel trapper. I tried my best to find the most "benevolent" one. But the problem here isn't the trapper, it is the animal itself. When I caught a squirrel, the poor thing started abrading itself by banging its nose against the cage. Animals aren't that different from us. How would you like it if you were put in a cage, or kept as a pet? After that incident, I did not harm the squirrels again. But now I share with them. I specifically leave a few fruits out for them in a special corner in which they seem to enjoy sitting. And as another bonus, they chase away the small birds that peck at every single fruit (they don't even eat them, apparently looking for worms inside). As for your mouse, unless it is causing property damage, like chewing through wires, then it would be best to leave it alone. I have seen a few mice rummaging around in my garage myself! But there was one thing I noticed; ever since the mice moved in, I haven't seen any bugs in my garage, except for the occasional spider. But spiders are a different topic. I used to enjoy killing spiders, until one day I was bit by a mosquito. I chased that thing all over the house, and it flew into my bathroom and I couldn't find it. The next day, I looked in the corner of the cabinet under the sink, and there was a fat mosquito stuck in a spiderweb =). Moral of the story: Weigh the benefits of having so-called "pests" around.--Kirby♥time 03:19, 16 May 2007 (UTC)

If the mouse is suckling young, its nipples will be more pronounced. Of course getting close enough to see this would be a challenge in a wild mouse. It will only suckle its pups for about 3 weeks, though, at which point they can fend for themselves. Even if you trap the mouse, the pups will likely survive for a significant time (perhaps about 5 hours if they are young, a day or so if they are a little older) without suckling, so you could always release her again and she could go back to feed her young. Do be careful though, as wild mice do harbor disease and they can give a nasty bite. Rockpocket 05:15, 16 May 2007 (UTC)

Wild mice continuously have babies. You can't dig them out of the compost, or trap them without disturbing a nest. Think of hantavirus when you want to let them live a happy life in your house. --Zeizmic 12:28, 16 May 2007 (UTC)

If you are considering letting it (and its possible friends) live happily in your house, consider that a mouse can give birth to litters of 6-8 pups after 3 weeks of gestation, and can get pregnant again within 24 hours of birth, and that those pups themselves become sexually mature after 6 weeks [9]. Do the math: two happy mice very rapidly become an astonishing number of mice. --mglg_(talk) 16:18, 16 May 2007 (UTC)

Years ago I discovered that a mouse had gnawed its way into a plastic bag of birdseed in the basement. I don't mind setting a trap that kills a mouse instantly. I do not like seeing a mouse with a trap snapped on its hind legs, trying desperately to drag its crippled body away. I object fundamentally to gluetraps, which are right up there with crucifixion. Poison leaves a dead animal somewhere out of sight stinking up the place. I decided to just catch and transport the villain. I built Trap 1.0 by putting away the bag of birdseed where he could not get at it, then leaving a trail of birdseed along an inclined plank which would lead him up to the top of a sturdy cardboard box, where a 1 foot ruler was carefully balanced across a dowel rod across the top, with a trail of birdseed. The next morning, I found that he had snarfed up the seed along the plank and walked across the ruler past the fulcrum, causing him to fall into the box. Then he gnawed his way out. Trap 2.0 was the same except I used a 5 gallon plastic bucket. The next morning, there he was in the bucket. I took him far away and let him go in the woods. Note that this will be contrary to the law in many jurisdictions. If you just take him outside, he will probably be back inside before you are. Edison 16:08, 16 May 2007 (UTC)

Humane mouse traps are really easy to make: http://www.smithsax.btinternet.co.uk/products.htm ...for example. Trap the mouse - drive a mile from your home and release it someplace. Pet mice are so cheap that our local pet store gives them away for free when you buy a mouse cage. That way you'll know it's healthy - and hopefully not pregnant. When I was a kid, my parents bought my sister and I two pet mice (both female) - both turned out to be pregnant - we had a total of 14 baby mice within no time. Those went back to the pet store as soon as they were running round with their eyes open. Personally, I'd get a hamster - they are not social animals - they like to live alone - Mice like to live in packs and it's probably not nice for them to live alone. SteveBaker 16:56, 16 May 2007 (UTC)

And as a bonus, hamsters can dance: [10]. StuRat 23:29, 16 May 2007 (UTC)

Do you have any idea how many years of intensive therapy it's taken to get that damned tune out of my head? Now it's right back in there again. My lawyers will be in touch! :-P SteveBaker 23:48, 16 May 2007 (UTC)

This may help somewhat. --Kurt Shaped Box 23:56, 16 May 2007 (UTC)

May 16

One Ounce

I was curious thinking about railguns and coilguns, if an object weighing one ounce was accelerated to 99% the speed of light how much damage could it do smacking into Earth? Or even would about an atom traveling at 99% the speed of light how much blow would that pack? —The preceding unsigned comment was added by 67.127.166.135 (talk) 00:25, 16 May 2007 (UTC).

You can calculate this using Newton's equation F=MA, where in this case, F is the force of the impact (in Newtons), M is the mass of the object, in Kilograms, and A is the deceleration of the object- in this case, 99% of the speed of light, divided by the time it takes for the object to come to a complete stop. For ease of calculation, I'll assume that a 100g object traveling at 99% of the speed of light comes to a complete stop in one second. In this case, the object would exert 29679453.342 Newtons of force on the earth. Ninja! 00:38, 16 May 2007 (UTC)

For ease of comprehension, this is roughly 6,672,238 pounds of force. Ninja! 00:41, 16 May 2007 (UTC)

I think a 1 sec decel time is too high, since it would travel 150,000 km in that much time. How about a 0.001 decel time, so it will stop in 150 km, instead ? In that case, multiply your answer by 1000. StuRat 00:56, 16 May 2007 (UTC)

More relevant than the force is the amount of energy dissipated in the impact. According to the Special relativity page, the kinetic energy (total energy minus rest energy) is $(\gamma -1)mc^{2}$ where $\gamma ={\frac {1}{\sqrt {1-(v/c)^{2}}}}$. Plugging in v/c=0.99 and a mass of 0.03 kg (about one ounce) gives a kinetic energy of 1.6x10¹⁶ J, which our Orders of magnitude (energy) page claims is comparable to the amount of energy dissipated by the meteorite impact that created Meteor Crater in Arizona. --mglg_(talk) 01:06, 16 May 2007 (UTC)

F=MA is not valid in relativity, see Special_relativity#Force. Icek 12:15, 16 May 2007 (UTC)

Wow, I am kind of disapointed that it doesn't plow through the Earth but hey Meteor Crater is a pretty massive hole. Thank you for the quick responce.67.127.166.135 01:23, 16 May 2007 (UTC)

As for the atom, it would just crash into an air molecule in the upper atmosphere and create a little shower of elementary particles. Most of those particles would decay on the way down, and only a few muons would reach the Earth's surface. Hydrogen and helium atoms (or at least their nuclei) traveling at highly relativistic speeds hit Earth in exactly this way all the time – see cosmic ray and Ultra-high-energy cosmic ray. --mglg_(talk) 01:33, 16 May 2007 (UTC)

Maybe we would get lucky and produce some antimatter!!!!!!!!!!!!!!67.127.166.135 05:18, 16 May 2007 (UTC)

Quite possibly - but that would immediately combine with some of the handy normal matter lying about the place and turn into a bunch of photons and probably, yet more exotic particles. Antimatter appears and is annihilated all the time, everywhere - it's not that odd. SteveBaker 11:34, 16 May 2007 (UTC)

Steve, you must be mistaken, look at the number of exclamation points. 213.48.15.234 13:57, 16 May 2007 (UTC)

I think it probable that antimatter would be created - there's a huge amount of energy involved, and a matter-antimatter pair can be made from a pair of high-energy photons (photons - which are the particles associated with light, x-rays, radio waves, etc - would very likely be created and be of high energy during high speed particle collisions, like in a supercollider). This might create, for example, an electron and a positron (anti-electron). Of course, as soon as these antimatter particles interact with normal matter, they will annihilate each other and will produce another pair of high-energy photons (gamma rays). The antiparticles will be very short-lived, probably disappearing in less than a second. --h2g2bob (talk) 14:44, 16 May 2007 (UTC)

It seems like it would resemble an H bomb explosion closer to the ground, except for the gamma rays and fallout. TNT equivalent says that a megaton of TNT is equivalent to 4.184 x 10¹⁵ J, so the energy stated above of 1.6 x10¹⁶ J would be equivalent to the detonation of a 3.8 megaton H-bomb. The Tunguska event is thought to be the result of a much larger asteroid travelling much slower, about 1/29700th as fast. The kinetic energy varies as the square of velocity and directly with mass, so the little projectile packs quite a punch for its size. The Tunguska object is estimated as tens of meters across, depending on composition. The Tunguska object is said to have been the equivalent of a 10-20 megaton nuke. There are eyewitness accounts of the Tunguska object from a survivor 40 miles away, who said it appeared as a fire which split the sky in two creating a wave of heat followed by a blast wave and huge noise. Of course no naturally occurring object in the universe is expected to be travelling at .99c relative to the earth (is it?), and we certainly have no present technology to impart that much energy and velocity to a 1 oz object. If you had a 1000 megawatt stationary nuclear plant working full time powering lasers to drive a space sail,and ignoring inefficiencies and losses and the object likely being vaporized by the focussed energy, it would take about 6 months to accelerate the object to .99c, if my math is right (no guarantees). That much solar energy would fall on a 1 kilometer square area of the moon in direct sunlight. Edison 17:10, 16 May 2007 (UTC)

Edison, re your statement/question Of course no naturally occurring object in the universe is expected to be travelling at .99c relative to the earth (is it?): If you count really small objects, there certainly are ones traveling very much faster than that relative to Earth. According to the article Ultra-high-energy cosmic ray, there have been at least 15 recorded instances of particles (protons?) hitting the Earth at speeds on the order of 0.999999999999999999999995 c. --mglg_(talk) 17:25, 16 May 2007 (UTC)

By "object" I was thinking of the 1 ounce hypothetical projectile. I would certainly extend the concept down to a BB, a paperclip, a Mustard seed, a flea, or a gossamer wing. I was not thinking of photons, protons, gamma rays, etc, which fall a bit short of my notion of "object". Edison 20:57, 16 May 2007 (UTC)

How much antimatter could be produced with the one ounce object, I wonder?67.126.131.253 05:06, 17 May 2007 (UTC)

1.6 x 10¹⁶ J/c² = 0.18 kg. That's the maximal amount of matter and antimatter created, and since the amounts must be equal, the maximal amount of antimatter would be 0.09 kg. That's only an upper limit, the amount created would probably be considerably less. Icek 08:35, 17 May 2007 (UTC)

What if, instead of a one-ounce object, you used a 1-cubic-centimeter section of a neutron star's core? Methinks that would be some serious carnage. - 2-16 14:03, 17 May 2007 (UTC)

Taking a middle value for density from the article, it looks like it's $3.5\times 10^{12}$ oz/cm³, so just multiply all the numbers by that. Of course, at that density and being so hard to stop, it might very well just pass through the Earth (in about 45 milliseconds) and leave a hole, rather than "explode" so much. --Tardis 15:06, 17 May 2007 (UTC)

Except that your chunk of neutron star would of course have exploded back to normal matter as soon as you took it out from the extreme pressure inside the neutron star. --mglg_(talk) 17:21, 18 May 2007 (UTC)

You're right, of course; I was just thinking about that substance, not its possibility. But there's still a solution; just move it so fast that in our reference frame it doesn't have time to explode! --Tardis 17:25, 18 May 2007 (UTC)

Macadamia nuts - inedible to everything except for man and parrot...

As I understand it (I was reading about this today), the only other animal besides man capable of cracking open a macadamia nut is the Hyacinth macaw. Considering that bird and tree live on different continents and never encounter each other in the wild, how is it then that the macadamia tree disperses its seeds? --Kurt Shaped Box 00:57, 16 May 2007 (UTC)

I would speculate that they fall off the tree and grow new trees right there. Lucky nuts might get washed down into a river and deposited in a nice place to grow. StuRat 01:14, 16 May 2007 (UTC)

I always thought that it was a Bad Thing for a tree's offspring to grow beside the parent - because of competition for nutrients and risk of pollination incest. I dunno, do these trees tend to grow on riverbanks? I've never actually seen one. --Kurt Shaped Box 01:25, 16 May 2007 (UTC)

It doesn't need to be on a river bank, a flood plain will do nicely. StuRat 03:08, 16 May 2007 (UTC)

Notice how you said "only other animal". Natural decomposition of the nut is not out of the question.--Kirby♥time 03:00, 16 May 2007 (UTC)

A HYACINTH MACAW CAN CRACK A MACADAMIA?!?!?! Are you serious??? I used a hammer and an industrial vice to crack those suckers after we broke our proper nut cracker on the 1st one. Vespine 07:07, 16 May 2007 (UTC)

Sure thing - video I found here. They're apparently a hyacinth macaw's favourite food. --Kurt Shaped Box 10:52, 16 May 2007 (UTC)

Just to be sure, I threw "macadamia seed dispersal" (without quotes), in Google (TM), and the first thing that came up was a JStor article about an Australian bird that disperses seeds: "However, some plant species, e.g., those of Macadamia, Dendrocnide and Aleurites, seem to be dependent on small indigenous rodents (mainly Rattus, Melomys, and Uromys spp.)..." The article is was called "Seed Dispersal by Cassowaries." I assume, like most seed dispersing animals, the birds and rodents (the article is a little unclear, it seems both may disperse the seeds) eat the flesh of the fruit and let the seed pass through (or discard it in the case of the rodent). Remember, if a bird actually eats the nut than there is nothing to germinate. Mystery solved thanks to Google (TM) once again. --Cody.Pope 08:19, 16 May 2007 (UTC)

Oh, of course! Thanks. I was thinking wrong - the macaws (and humans!) go against the plant's 'wishes' by simply destroying the entire fruit. Presumably the macadamia evolved such a tough coating to avoid this very situation with the local parrots and cockatoos, which are less powerful in the beak department. --Kurt Shaped Box 13:38, 16 May 2007 (UTC)

Have you seen "Clever Crows" on Google video? It may well be that these crows would be able to eat Macadamia nuts as well.

Atlant 11:44, 17 May 2007 (UTC)

Intelligent Design, my wagon!

Please explain to me the evolutionary history of hair on the behind... what purpose does it serve other than to stick to the exit crowd and cause a lot of pain?--Kirby♥time 01:31, 16 May 2007 (UTC)

http://www.skidmore.edu/scope/spring2004/features/hair.html David D. (Talk) 02:44, 16 May 2007 (UTC)

Potentially offensive comment moved here: [11]. StuRat 03:12, 16 May 2007 (UTC)

Well, we used to be hairy all over, for warmth, I assume. We've lost most of our hair, actually, so it's not that hair on the behind serves a specific purpose, but instead it hasn't been detrimental enough for it to be selected against. Wait a few hundred thousand years, and maybe butt hair will be gone. ;-) zafiroblue05 | Talk 02:46, 16 May 2007 (UTC)

They actually have a scientific name, you know: perianal hair (which we don't have an article on, unsurprisingly). Rockpocket 05:09, 16 May 2007 (UTC)

Potentially offensive comment #2 moved here: [12]. StuRat 03:12, 16 May 2007 (UTC)

Kinda like eyelashes for the butt, to keep detritus and pathogens from entering the rectum? Or, pubic hair informs me that perianal hair is androgenic, and does not show up until the pubarche stage of puberty; perhaps, then, its appearance is due to some quirk of biological similarity between the anal region and the places where androgenic hair actually does/did serve some purpose? Butt all this is just shooting in the dark. Eldereft 06:29, 16 May 2007 (UTC)

Didn't read your comment before I posted below, but I agree on the significance of the location/age of perianal hair growth vis-a-vis pubic regions. --Cody.Pope 08:48, 16 May 2007 (UTC)

Just to add-in here: humans didn't "lose their hair" per se, we still have the same amount of hair follicles as you'd expect on a big mammal, it's just that our hair isn't as long/thick. So the real question is, why did we keep long hair there? And the best answer that I can some up with is the old pheromonal argument for underarm/pubic hair -- that region is just close enough to retain some hair (perhaps even controlled by the same region of genes, in so much as losing perianal hair might mean losing pubic hair as well, but that's just speculation). I've also heard Nurse Sue of Talk Sex claim that pubic hair helps reduce friction during copulation, but not sure how that would apply here. --Cody.Pope 08:00, 16 May 2007 (UTC)

Proof of Potential Difference and Resistance Formula

Hello. Can anybody prove the potential difference formula, V = E/Q and the electrical resistance formula, V = I * R? Thanks. --Mayfare 02:48, 16 May 2007 (UTC)

I'm not sure the former needs to be proven since it's just the basic definition of a certain physical quantity we call electrical potential. The latter is also just a definition; resistance is defined as the amount of electrical potential drop per unit current. In terms of the linear behavior implied (a constant R), it becomes more of an observation that somewhat holds on the macro scale, it being the definition of a certain type of current-voltage characteristic observed in many circumstances (so-called "ohmic" behavior). -- mattb 03:48, 16 May 2007 (UTC)

See Maxwell equations. The divergence of the electric field equals the charge enclosed. From that 1st principle and the magnetic field equaiton (del cross H), Ohm's law can be derived. --Tbeatty 04:00, 16 May 2007 (UTC)

Spiders of Oregon

We were working in the yard tonight and saw a mean looking spider. It looked like a black widow, but less intensely black, more of a dark chocolate brown. It did not appear to have the red hourglass either. We thought maybe brown recluse, but apparently these are not endemic to Oregon. We live just outise of Portland. Any other thoughts on what the species of spider this might have been? thanks! —Gaff ^ταλκ 02:59, 16 May 2007 (UTC)

Maybe a brown widow? Wiwaxia 04:56, 16 May 2007 (UTC)

hmm...at first I thought this was a joke reply. But then I looked it up. According to WP, the brown widow, Latrodectus geometricus, does not live in Oreogn. Thanks though.—Gaff ^ταλκ 05:40, 16 May 2007 (UTC)

False black widow? --24.147.86.187 13:04, 16 May 2007 (UTC)

I am in the same area as OP, I bet it is Neoscona arabesca or a similar species of orb weaver. They are found just about everywhere in North and Central America. Google that name for some pics, they look a lot like the ones I have in my yard. 161.222.160.8 23:35, 17 May 2007 (UTC)

Evaporation of Raid

How long does it take Raid to completely evaporate after it is sprayed? Wiwaxia 04:56, 16 May 2007 (UTC)

I don't think insecticide really evaporates, if you mean how long before you can't smell it? or how long before it won't kill insects any more? Those questions are highly subjective and they would depend on many things like the size of the room, if a window or door is opened, what kind of insects you are killing, whether you are spraying it on a surface. I'm sure the company that makes it will make all sorts of claims about useful lethal duration and stuff but I'm sure you'll find their claims are just high estimates. Vespine 07:01, 16 May 2007 (UTC)

My mother told me that Raid actually evaporates rather than just losing its potency, and that it is highly "volatile". Wiwaxia 06:22, 17 May 2007 (UTC)

If you follow the links from the article you can ask them yourself.--Shantavira 08:13, 16 May 2007 (UTC)

It's likely that the water content evaporates quickly, while oily residues and other complex chemicals which were in solution may stay behind "indefinitely" (at least, on time-scales compared to water evaporation). Nimur 08:41, 16 May 2007 (UTC)

Bitten cat

what to do if a house cat gets bitten by a black widow?— Preceding unsigned comment added by 72.193.165.80 (talk • contribs)

Take it to the vet immediately. --Cody.Pope 09:30, 16 May 2007 (UTC)

Cobras

How can we get rid of Asian cobras under our house in Krabi, Thailand. We have seen several large skins. —The preceding unsigned comment was added by 222.123.98.98 (talk) 09:11, 16 May 2007 (UTC).

Dunno about Cobras and I've never been to Thailand - but here in Texas, the usual cause of large poisonous snakes taking up residence is because you also have a rodent infestation. According to our article on cobras, King cobras eat other snakes - it doesn't say what other cobras eat - but they are carnivores - so I'd bet that rodents are a large fraction of their diet. Get rid of the rats and mice - and the snakes will leave to look for food elsewhere. So I'd definitely try rat and mouse poison. But if you havn't seen any actual snakes, it's possible that the cobras just like the space under your house for shedding their skins - and that they leave to hunt elsewhere between shedding. If all else fails, I guess you could get a Mongoose. SteveBaker 11:25, 16 May 2007 (UTC)

Put them on a one-way flight to Los Angeles. - 2-16 12:42, 16 May 2007 (UTC)

lol!! Rangermike 14:48, 16 May 2007 (UTC)

It would kind of have to be a one-way trip, wouldn't it ? Who would want to take the return trip on that airline ? ("...well, they did have good peanuts"). StuRat 23:14, 16 May 2007 (UTC)

put them on a plane with Samuel Jackson "will someone get these damn snakes off the plane!" lol!--Lerdthenerd 08:23, 17 May 2007 (UTC)

Use of flowers

I kindly request you to tell me uses of the rose and the jasmine(mogra) flower. Are these flowers used for pollination? If yes then do these plants produce seeds?

-I will be very grateful to you for answering this question? _____________________________Thanking you________________________ 202.71.137.235 12:11, 16 May 2007 (UTC)Hemchandra

AFAIK all flowers are used for pollination, then produce seeds, that's their entire purpose. StuRat 23:09, 16 May 2007 (UTC)

(After edit conflict) I don't understand your question. Especially, the question if these flowers are used for pollination looks somewhat odd. Flowers do pollinate each other if they are genetically close to each other (that's to say, of the same kind). The actual carrying of the pollen is done mostly by insects, or by wind.

Could you please rephrase your question? 84.160.208.134 23:29, 16 May 2007 (UTC)

Flowers can also be useful in human "pollination".

Atlant 11:48, 17 May 2007 (UTC)

calotropis gigantia

why do snakes love this plant. 202.71.137.235 12:13, 16 May 2007 (UTC)Thx Raaaaaaajukumaaaar

do they? I could find no reference to that fact. If you have any reference or link to give, by all means please do. BTW the correct spelling is Calotropis gigantea, not gigantia. The plant is used in traditional medicine to treat snakebite [13], but I found nothing on snakes being attracted to it. Cheers, Dr_Dima.

Physics

Why doesn't the frequency change from one medium to another while wavelength does? —The preceding unsigned comment was added by 210.212.10.130 (talk) 14:30, 16 May 2007 (UTC).

The frequency of a wave (how many oscillations it makes per second) must everywhere stay the same as the frequency of the source that produced the wave. If you think of a loudspeaker membrane making a sound wave, for instance, it does so by vibrating in and out with some period T. Since the motion is periodic, there is no difference between the 1000000^th time the membrane reaches its maximum-out position and the 1000001^st time it does so, a time T later. Since there is no difference at the source between those times, there should be no difference anywhere else in the propagating wave either between those times. Therefore the whole wave is periodic in time with period T, or, in other words, it has a frequency f=1/T everywhere. The wavelength, on the other hand, is the distance the wave propagates in the period time T, which is T times the propagation speed. If the wave enters a medium with a lower propagation speed, it will travel a shorter distance in the period time T, so its wavelength in that medium will decrease. --mglg_(talk) 15:58, 16 May 2007 (UTC)

Your answer is of course true, but the very notion that "no difference at the source" implies "no difference anywhere else" is a non-trivial result of linearity. All linear operations on a sinusoid, which is a pure frequency, yield other sinusoids (albeit perhaps with different amplitudes and phases) with the same frequency. Non-linear systems can and do change the frequencies of waves interacting with them; see frequency doubling for example. --Tardis 16:43, 16 May 2007 (UTC)

Well, it is a trivial result that periodicity with period T at the source implies periodicity with period T throughout the wave (assuming that there are no other time-varying things that could cause Doppler shifts etc.): this is just a statement of invariance under time translation by T. As you point out, nonlinearities can distort an originally sinusoidal wave so that it comes to contain harmonics of the source frequency, but the distorted wave is still periodic with period T, and has the same fundamental frequency 1/T as the source (except for the special case when the nonlinearity exactly eliminates the fundamental). --mglg_(talk) 19:17, 16 May 2007 (UTC)

For a (general) non-linear system I don't think you can claim that just because the source is invariant the effect has the same invariance: the medium can have memory and hysteresis and all sorts of ugly effects that just don't settle out even over infinite driving time. Do correct me if I'm wrong; is it in fact always the case that such effects are transient? --Tardis 22:42, 16 May 2007 (UTC)

You can also look at the math: Velocity = Frequency x Wavelength. So when the speed of the wave changes because it passed into a different medium, the wavelength changes by the same amount (eg if the speed doubles, the wavelength doubles) hence, the frequency has to stay the same in order to keep the equation balanced. SteveBaker 16:43, 16 May 2007 (UTC)

This is a very good question. As long as oscillations are small, indeed, the frequency does not change as mglg explained above. However, in case when the oscillations become rather large (such that there is a substantial difference in properties of the medium at different phases of the wave) the frequency may change: harmonics may be produced. Imagine a microphone. The air vibrations are picked up by the microphone membrane. Assuming the sound wave has only a single frequency w, the air pressure in the sound wave is proportional to sin(wt). As long as the sound volume is not too high, the membrane position will be proportional to sin(wt+f₀) where f₀ is a constant phase shift. The frequency w is the same. However, when sound becomes very loud, the membrane vibration amplitude becomes quite large and affects the membrane elasticity. Such a motion is no longer sinusoidal, and contains other frequencies besides w (usually 2w, 3w, ...). In acoustics and electronics that effect is generally called distortion; you can hear the reproduced sound becoming "dirty". For electromagnetic wave you may look at frequency doubling or at nonlinear optics in general. So, the frequency does not change in a weak ("linear") oscillation regime; but it can change (or, more accurately, new frequencies may appear while the original frequency still remains, as well) if oscillations are strong ("nonlinear"). If you have any further questions, please do not hesitate to ask. Best wishes, Dr_Dima.

Yes indeed this is a very interesting question, and one with which I have been struggling for quite a few years now. It seems that in wave propagation, frequency is the only invariant. Wavelength and velocity are related by v = f * lambda. Apart from the doppler phenomenon (that requires a moving source or reciever), it would appear that frequency cannot be changed 'on the fly'. It may, however, be possible to change the frequency of a short duration signal by somehow altering the velocity of propagation of a 'captured' wave.

As I understand it, the original wave induces oscillations at the same frequency in nearby electrons, and the new wavelength comes about by adding the original wave to the dipole radiation thus produced. Summing sinusoidals of the same frequency can produce changes in wavelength and amplitude, but not frequency. Nonlinearities enter naturally when the dipole part of the oscillating electrons is no longer a sufficient description. Eldereft 04:01, 17 May 2007 (UTC)

A simple way to look at it is to think about what happens at the boundary between two materials. The frequency determines how many wavefronts are both entering and leaving the boundary. What happen's if frequency changes? Somehow the boundary would have to create or store wavefronts, to adjust for the change in frequency, I think you'll see this is a strange idea. Cyta 07:28, 17 May 2007 (UTC)

A simple question but a really good thinking point!

Propagation of waves is all determined by local continuity conditions - adjacent oscillations in time and space have to link up with their neighbours in a well-defined way, as expressed by the wave equation.

The most familiar situation with light is where a wave passes from one medium into another with a different refractive index, where its speed is different. Here we have a system in which the properties of the medium are constant in time, but not uniform in space. To accommodate the change in wave speed, the spatial part of the wave has to adapt - so the wavelength changes. This gives us a constant frequency, with varying wavelength, and this case is well explained above. Non-linearities can introduce extra frequencies, but they are still harmonically related to the original.

But what happens if you have the reverse situation: a medium which is uniform through space, but whose properties change, everywhere at once, as a function of time? The initial conditions would dictate that the wavelength must remain unaltered, but the frequency would have to change to adapt. We would then have a constant wavelength, but varying frequency. (The maths is practically the same; we are just interchanging the time and the space coordinates).

A familiar one-dimensional example is altering the tension on a violin string while it is vibrating - wavelength remains constant, but the pitch varies. It would happen with a travelling wave as well as with a standing wave. The corresponding phenomenon with light is not so common, because it's difficult to capture a wave for long, but not impossible. You could do it, as Eldereft hints, by using an electro-optic medium inside a Fabry-Perot resonator, and changing its refractive index in a time short compared to the storage time of the resonator. (I know systems like this are studied quite extensively, but unfortunately that's all I know about them.)

If we allow the properties of the medium to oscillate with time (rather than just undergoing a step change), then there are several examples of changing-frequency effects. The common acousto-optic modulator shifts light frequency by a continuously controllable amount, using the diffraction of light from a moving sound wave: Doppler effect from one point of view, photon-phonon scattering from another. Raman scattering changes the frequency of light by reradiation from vibrating molecules. So, in a spatially homogeneous medium, time variations can lead to frequency variations.

In real life, we have three space coordinates to play with and run backwards and forwards in, and only one time coordinate that happens to be fairly inflexible. This may be why the frequency change effects are less familiar. --Prophys 11:24, 17 May 2007 (UTC)

acyldipeptide

I'd like to know the general structure of an acyldipeptide. Yes, I've googled it. Yes, I know what a dipeptide is. What I am unsure of is exactly what modification the acyl refers to. Where is it attached? ike9898 15:03, 16 May 2007 (UTC)

I assume we're talking about N-acyldipeptides (i.e., the ones listed by googling for "acyldipeptide"). That "N" tells you that it is a nitrogen that is acylated. A simple N-acyldipeptide would be N-acetyldiglycine: CH₃-CO-NH-CH₂-CO-NH-CH₂-COOH DMacks 15:36, 16 May 2007 (UTC)

Thanks! ike9898 15:57, 16 May 2007 (UTC)

Basal Metabolic Rate Question

Good morning,

I'm hoping that someone can clarify the Basal Metabolic Rate article for me, specifically BMR's effect on weight loss. I found the BMR article a tad confusing. To illustrate my question, I calculated the BMR for the "average male" at the Discovery Health's website BMR Calculator. Assuming a 25 year old, 175 lb, 5'10" male, the BMR is about 1,875 calories. So, this means that, at minimum, this male would need to consume roughly 1,875 calories per day just to sustain life? Additionally, assuming that the man consumed less than 1,875 calories, there would be a "calorie deficit" resulting in weight loss (with everything else being equal)?

I guess I'm not seeing the BMR's connection to weight loss. Maybe I'm overanalyzing.

Thanks! Rangermike 15:33, 16 May 2007 (UTC)

It seems to me that you have explained things very well, so I'm not sure what you don't understand. The BMR is essentially how much energy gets used up with no exercise counted. If you consume food containing less energy than that, then your body needs to get the additional energy it needs from somewhere. The usual place is the body's fat stores. When fat goes away, you weigh less. Thus, weight loss. --Tugbug 17:55, 16 May 2007 (UTC)

Your caloric intake doesn't need to be lower than your BMR to lose weight. BMR assumes that the person is in rest. Most of us move around if only a little. So to be clear, to lose weight, you need to consume less calories each day than you spend in that day . Of course in a sense your body IS consuming those calories, if by consume you mean taking fat/protein that is available in the body and burning that off.

so assume I'm a somewhat active person. I use about 2500 calories each day. I eat about 2000 calories worth of food. I'm left with 500 calories worth of deficit. Those calories get taken out of your fat stores and available protein. And you then lose weight PvT 20:18, 16 May 2007 (UTC)

It's not quite that simple. Your body will interpret insufficient calories as meaning you are starving to death, and will take action to save your life. It will make you think about nothing but food and shut down or reduce all optional systems to save energy. In this starvation mode you will then burn far fewer calories, and you will be listless, extremely hungry, unable to think clearly, stop growing (if a child), uninterested in sex, sleep more, need to keep your temperature up or shiver uncontrollably, etc. StuRat 22:10, 16 May 2007 (UTC)

Very interesting discussion, I apprecaite the reply! Rangermike 12:34, 17 May 2007 (UTC)

Lightning Strike

Any idea how lightning does not create an EMP wave unlike an EMP weapon or a nuke? 59.92.247.166

Well, lightning and nuclear weapons are entirely different things, much as how Quizno's doesn't create SUVs like General Motors. Is there some further point of clarification that needs to be addressed? — Lomn 15:58, 16 May 2007 (UTC)

Lightning does create EMP. --mglg_(talk) 16:03, 16 May 2007 (UTC)

An EMP (an Electromagnetic Pulse) is just a burst of electromagnetic waves - technically, turning a flashlight on and off again creates an EMP. I suspect that our questioner wishes to know whether the EMP is large enough to do massive destruction to nearby electronics and such. Clearly the EMP from a flashlight isn't - and the EMP from a nuclear explosion is. Somewhere between those two extremes lives the lightning strike. It's just a matter of degree. Since the intensity of omnidirectional electromagnetic waves drops off as the square of the range - a lot depends on how close you are to the source. If you are really close to a lightning bolt, I would expect the size of the electric field would be plenty big enough to cause a damaging voltage difference across the pins of a delicate silicon chip - but probably not enough to destroy the ignition circuitry of a car...it's a matter of range and intensity though - there isn't a black-and-white answer here. SteveBaker 16:37, 16 May 2007 (UTC)

Minor nitpicker's correction: A bolt of lightening is a linearly extended source of EM radiation, and hence, the field falls of linearly with the distance, not with its square. And yes, your electronics will get damaged if your neighbors house is struck by lightening, unless you use surge protectors or are lucky. Simon A. 19:09, 16 May 2007 (UTC)

Geez, last night we had a monster storm, and then one of those instant lightning strokes without thunder (too close!). I could hear all the surge protectors pop, as the power went out, almost like an explosion! Lost one surge protector, and one old ethernet switch. --Zeizmic 20:39, 16 May 2007 (UTC)

Have you done something to anger God ? Just feel lucky that His aim isn't better. :-) StuRat 23:04, 16 May 2007 (UTC)

We got a melted TV due to a close bolt. I love that smell! 213.48.15.234 07:59, 17 May 2007 (UTC)

Stability

Any idea on how do we model stability and how do we decide modes of resonance on systems such as rockets, planes, and other control systems??59.92.247.166

That's a homework question if ever I saw one. Flight dynamics might give you a starting point. --YFB ¿ 16:43, 16 May 2007 (UTC)

A static model wouldn't work, so you'd need a complex dynamic model, perhaps using fluid dynamics software to model turbulent flow. StuRat 22:57, 16 May 2007 (UTC)

To do it practically you can use a wind tunnel, either with the real thing or a scaled down model. As fluid dynamic systems are often chaotic and difficult to model mathematically, I suspect an experimental approach is used in conjunction with theoretical models. Cyta 07:31, 17 May 2007 (UTC)

Fuse

We know that a fuse wire melts due to overheating.But the practical resistance of a fuse is low. So how does that become equivalent to heat in melting the fuse, because P=i^2r? Also would it not cause a voltage drop?? How does the voltage drop suddenly increase when the fuse is about to blow and its negligible when the fuse is operated under max current rating??Also any idea how do same value and different wattage restistace work??59.92.247.166 15:52, 16 May 2007 (UTC)

It is unclear what you mean by "same value and different resistance wattage." If you solve some problems in basic Ohm's Law it may become clearer to you, or clarify the question. A Fuse (electrical) is made of a material with a lower melting point and a higher resistance per unit length than the conductor it protects. It was noted in the mid-1800's that if you connect a piece of iron wire and a piece of copper wire of the same size in series and pass (obviously the same) current through them, the iron wire will get red hot and even incandescent while the copper wire is not. A fuse wire does not get red hot because it melts first. So a 1/3 inch piece of small diameter low melting point alloy, like fine solder, will carry an amount of current without melting which an insulated copper conductor can carry without exceeding the rating of the copper (say 15 amps for number 14 copper). If the current goes a certain amount over 15 amps, the fuseheats up (the power dissipated in it is given by the current squared times the resistance) and softens and melts, interrupting the current and preventing the copper wire from starting a fire. This is of course contingent onthe fuse device design, to be adequate for the voltage level and the available fault current. The copper need not get nearly as hot as the fuse wire, which has a much lower melting point anyway. As for voltage drop, remember that the fusewire is very short. It has a higher resistance per unit length than the copper, but it is very short, so the total resistance it adds to the circuit is very slight. The voltage drop equals the current times the total resistance of the fusewire, and that resistance is proportional to the the very short length, hence a very small voltage drop in the fuse under normal operation. The first fuses were literally a solder-like alloy, and were connected between 2 screws or clamps. I have seen an ancient spool of 15 amp fuse wire. Today they are fancier, in cylindrical cartridges, screw-in plug fuses, in oil filled cylinders or sand filled cylinders for high voltage. Their melting and clearing time-current curves are studied by engineers so that they coordinate, meaning that the downstream fuse closest to the fault (short circuit) should clear before the upstream (backup) fuse, to minimize the circuitry deenergized. Edison 17:33, 16 May 2007 (UTC)

Yes. Also to answer the other Q, since metals usually have a positive temperature coefficient of resistance,(ie resistance goes up with temp), then under fault conditions, the fuse gets warm, increases its resistance and therefore gets even warmer (assuming the current is constant). This positive feedback phenomenon should cuase the fuse to blow more quickly on large overloads. It is worth noting though, that a fuse will take an infinite time to clear at its 'rated' current and still a long time to blow even if slightly overloaded.

This exact question was asked (and answered) about a week ago on one of the Reference Desks.

Atlant 11:55, 17 May 2007 (UTC)

platelets

platelet structure,its surface receptors?what is aggregometry —The preceding unsigned comment was added by 59.93.204.58 (talk) 16:26, 16 May 2007 (UTC).

Wikipedia's article platelet appears not to cover aggregometry, but according to Google it refers to the measuring of aggregation of platelets. You put some blood or platelet-rich-plasma in a test tube, add something that ought to activate the platelets, and measure how fast they clump together. Algebraist 16:58, 16 May 2007 (UTC)

In the U.S., at least, these would generally be referred to as platelet function tests, rather than the highfalutin' aggregometry. We don't have articles, but you can get a good overview here. - Nunh-huh 11:27, 17 May 2007 (UTC)

math

If I had an object weighting 1kg, and applyed an upward force of 9.8065...N on it, would it stay exactly where it is and appear to weight nothing, or would it move upward at 9.8065... ms-2?

If you do this experiment on Earth's surface, the object would stay where it is. In fact, if you just let the object sit on the ground, the ground will push it upwards with exactly that force, which is why the object does stay put even though gravity is pulling it downward. If instead you did the same experiment in space, far away from any sources of gravity, your object would accelerate at the rate you mentioned. --mglg_(talk) 18:42, 16 May 2007 (UTC)

So, if I applyed a stronger force it would move upward, then if I switched back to 9.8065...N it would stay were it was? A related question-is there any relationship between force, pressure and torque? And what is it?

F = ma (apologies if the cases are incorrect). F, in this case, is net force (gravity and your imposed force). When F is non-zero (when you apply the stronger force), the object accelerates. When F returns to zero (you apply the 9.8...N force), acceleration returns to zero. Velocity stays where it currently is (assuming no air resistance, change in gravitational field, etc). — Lomn 20:01, 16 May 2007 (UTC)

(After edit conflict) Yes, it would accelerate upward if you applied a stronger force. When you switched back, it would stop accelerating, but would keep going upward at a constant speed. Eventually it would get high enough that Earth's gravity would start to weaken noticeably, at which point the object would be slightly accelerating because your force was no longer being completely canceled by gravity. As for the relationships, see force, pressure and torque. Basically, pressure=force/area and torque=force*(lever arm length). --mglg_(talk) 20:03, 16 May 2007 (UTC)

hmm So Pressure is like a force density, and Torque is a force multiplier...? -Czmtzc 20:38, 16 May 2007 (UTC)

Say rather torque is a rotational force. Algebraist 22:32, 16 May 2007 (UTC)

Psychokinesis/Psychic Abilities

Are there any hard evidence of anyone possessing these abilities that were scientically proven? Is there a way for one to train oneself for these? --Juliet 18:49, 16 May 2007 (UTC)

No, and no. --mglg_(talk) 18:43, 16 May 2007 (UTC)

How do you know, mglg?--Juliet 18:55, 16 May 2007 (UTC)

It seems as though the Psychokinesis article has lots of information on studies; have you checked it/them thoroughly? Anchoress 18:51, 16 May 2007 (UTC)

I was hoping that someone in the AMA (American Medical Association) had proven it somehow....--Juliet 18:53, 16 May 2007 (UTC)

actually no and yes. I'm learning, but very slowly :( Ask again in a few months and it might be yes and yes :] HS7 19:20, 16 May 2007 (UTC)

Nobody has claimed the million dollars James Randi offers to anyone who can demonstrate psychic abilities. Clarityfiend 19:53, 16 May 2007 (UTC)

No for both questions. they're many reasons why people claim they have such powers... but there's just zero scientific evidence of either. in the case of the second one, its largely a matter of commercialy exploiting people who will buy it. in other words, scammers. the con artists are sometimes a good judge of character/situation and thats why they sometimes seem to have some substance to their services but there's nothing supernatural about that.  Adam2288  T  C  21:45, 16 May 2007 (UTC)

Of course there is hard evidence. I can make the head of any attractive girl turn the other way. Um, does that not somehow match the definition of psychokinesis? Perhaps more psycho than kinesis? ;-) 84.160.208.134 22:45, 16 May 2007 (UTC)

I wonder if those with psychokinesis find it any easier to drag themselves out of bed in the morning. StuRat 22:54, 16 May 2007 (UTC)

The second most horrifying dream I ever had was that I got up in the morning, labourously and exhausting as ever, and then to awake to real reality, just to find all that toil is still ahead. The uttermost horrifying dream, frequently as a child but long gone now, was that the curtains were moving and I found out that it was me, moving the curtains by psychokinesis. Sure I didn't know the word then, but sure as hell I knew perfectly well the idea of it. Never found out why it was so horrifying, though. That it was uncontrolable doesn't account for all the horror I felt. 84.160.208.134 23:57, 16 May 2007 (UTC)

Speaking of dreams, you might try Lucid Dreaming, it's probably the closest you can come to actual psipowers. -- Phoeba Wright^OBJECTION! 02:16, 17 May 2007 (UTC)

Whoever believes in psychokinesis, raise my hand! — Kieff | Talk 02:20, 17 May 2007 (UTC)

I think the art of conning is actually a much more interesting phenomenon than psychokinesis. It is amazing how somebody of intelligence can be persuaded of almost anything. Conning is a real and provable phenomenon; it happens every day amongst members of every socioeconomic stratus. Psychokinesis is a form of conning, but it is only a sub-set of a larger techniques. People are able to convince others of virtually anything, whether it involves magic, mental powers, or beach-front time-shares. Nimur 04:45, 17 May 2007 (UTC)

Why does everyone dissagree with me here :( Just because I can't proove it yet, doesn't mean it isn't real :) HS7 18:32, 17 May 2007 (UTC)

And you have to be famous to claim the $1,000,000 prize :( HS7 18:33, 17 May 2007 (UTC)

No, you simply have to demonstrate, to scientific standards, that it works. If you do that, I assure you that you would instantly become famous! --169.230.94.28 20:59, 17 May 2007 (UTC)

Finally dreams can be inexplicably horrible for no reason :( The scariest dream I ever had was of a small black cloud floating across the room :@ HS7 18:35, 17 May 2007 (UTC)

Floating Shoes

Assuming someone wanted to make 'shoes' that floated, (taking the rollerblade/heelies idea to a whole new level) what would be the most viable and feasible technology to do so? I'm thinking something that works akin to the Segway, where leaning changes direction...and also, for balance, the feet positioning would be one foot forward, one back, bike-style. Which tech would accomplish this? fans? anti-grav? magnets? 140.180.11.227 21:56, 16 May 2007 (UTC)

There's 2 options i can think of, both of which wouldnt be very practical. 1: true floating shoes with air cavities would have to be large enough do displace the rider's weight worth of water, roughly 20-50 liters (5-13 gallons) on each foot.. thats gonna make them huge.. it would be hard to qualify them as shoes, more like big pods under your feet. option 2: power floating you can have some kind of thrusters under it, so its essentially some kind of jet pack that makes u stand in water. again, the size is gonna be a big problem, unless you carry the engine part on your back and have tubes connecting to the shoes. using pulling water into the backpack and thrusting it back out through a tube system connecting to your feet... thats deviating quite a bit from "shoes" now isnt it? makes for an interesting invention nonetheless. if you ever get it to work, i might even buy one myself.  Adam2288  T  C  22:05, 16 May 2007 (UTC)

Perhaps floating shoes on mercury would work a bit better. StuRat 22:48, 16 May 2007 (UTC)

How about a heavy keel as a counterweight below the shoes for stability? --User:bmk

Certainly people have made these many times in the past - there are even contests for them. Mythbusters tried to make some and failed - but they made a few critical boo-boos.

1. The "shoes" have to be big boxes - the length of ski's - 20cms wide - 10cms deep - two meters long. Probably made of foam polystyrene stiffened with somelightweight material. They need to displace enough water to equal the weight of the person wearing them. 0.2x0.1x2.0m is 40liters - or 40kg of water per shoe. Two of 'em will support 80kg...so if you weigh more than that - think bigger!
2. It's almost impossible to keep the shoes (think 'skis') parallel in a zero friction environment. This means that you need something like a pair of short bungee cords strung between the fore and aft tips of the ski's to keep them more or less parallel.
3. In order to get some kind of forward propulsion as you walk, there need to be soft rear-facing pockets on the undersides of the shoes that open up and catch water as the shoe tries to slide backwards in the water - whilst collapsing shut when the shoe slides forward. Thus, as you slide your feet back and forth, the backward-going foot has lots of 'drag' so it doesn't slip back so far - whilst the forward-going foot slips easily through the water. Without that you'll just be shuffling your feet back and forth and going nowhere.
4. It's quite hard to get started with the shoes - you'll probably need to enter the water from a gently shelving beach.

SteveBaker 23:37, 16 May 2007 (UTC)

How about you improve on their design? If I could find some in my size (fsking 8EE) that WEREN'T A PAIN TO USE, I'd be right on it. -- Phoeba Wright^OBJECTION! 02:14, 17 May 2007 (UTC)

The most simple, if not the most feasible, answer is in the thread directly above. Check in with the 'PK apprentices' in a few months, they may be able to get something going for you. Anchoress 02:22, 17 May 2007 (UTC)

I read about a 19th century inventor who built float shoes. Each foot had a shoe which looked like a little canoe with a top(airtight). There were flaps on the bottom, I believe, which folded flat on the forward stroke and popped down to resist the water on the backward stroke. The feet may have been in hinged shoes to make it easier to move the feet back and forth. He claimed he was walking the length of the Mississippi River or some such, and people would turn out to see him walk on water past each town. A reporter said he made his way very slowly and shakily past the town. The reporter suspected that he had assistance getting between towns. I agree about the need to keep the shoes from moving apart. A sliding linkage betwen the shoes, like a drawer glide, would keep them parallel. Then you might need a rudder or just the ability to keep one stationary and propel with the other to make turns. A reverse feature might involve changing the flap so it latched for forward or reverse operation, so you could turn on a dime. It should work after a fashion, but not making use of the upper body would limit speed, since the legs would pretty much be doing all the work. Taking it a step further, if it really doesn't have to look like a pair of shoes, consider a lightweight version of the Nordic Trak wherein the arms and legs are contributing to the propulsion. There could be a rudder on each float controlled by a handgrip. Edison 14:07, 17 May 2007 (UTC)

On further research: see [14] about a modern inventor of modern shoe-kayaks and the aforementioned H.R. Rowlands who was the 1858 inventor at [15]. Edison 20:52, 17 May 2007 (UTC)

Weird question

ok, here's a poser - I'm writing a bit of prose set in Hell - it's in a stone chamber so ancient that the screams of the damned have eroded the walls. The question is: would the erosion adopt particular shapes - would there be peaks and troughs - nodes at the points where the soundwaves focused to gouge deeper hollows in the stone?

Ta

Adambrowne666 23:13, 16 May 2007 (UTC)

Creepy! Interesting idea - I think there would be patterns on the wall determined by the dominant sound modes in the room from the spectra of the screams of the damned. However, I think in reality other factors would erode the walls much faster than screams. Like the flailing of the damned. Or the moisture erosion from the breath of the damned. Anywho, it's Hell, so I guess your guess is as good as mine. -User:bmk

If it helps the story - we can cook up a plausible sounding reason! The loudest sounds would be at the resonant frequency of the chamber - so we could certainly imagine an effect whereby the wall eroded much like a washboard road. Over the millenia, the washboarding might even add interesting overtones to the sound - perhaps making it sound ever more blood curdling as time goes on? Yeah - I could buy that. Probably it would end up looking like the ripples in sand on a beach. SteveBaker 23:25, 16 May 2007 (UTC)

Of course, assuming the physics of Hell is the same as up top, then the mechanism is dynamic spalling [16] caused by sonic waves, or impact of energetic ectoplasm. This would tend to follow the structure of the rocks (joints, faults, etc), so you could write 'the torture of the rock made so plain, etc'. --Zeizmic 00:20, 17 May 2007 (UTC)

Thanks so much, guys, for taking the question in the spirit in which it was intended - your answers are perfect, extremely helpful -exactly the kind of stuff I was hoping for Adambrowne666 10:50, 17 May 2007 (UTC)

A PDS (Poor Damned Soul) might just sit/stand/lie in one place and shriek in eternal torment (there would doubtless be no icewater to drink, thus no bathroom breaks needed). In that case he would generate sound energies which would doubtless cause over eternity erosion of the interior surface at the locations where the sound waves of his shrieks cause the greatest amplitude of vibration, perhaps looking on the walls floor and ceiling something like the appearance of an egg carton. On the other hand he might not be restrained, so the erosion might be more diffused if he followed my motto: "When in trouble, when in doubt, run in circles and scream and shout." In that case the erosion pattern might be annular. Edison 13:56, 17 May 2007 (UTC)

Assuming most screams are in the falsetto or whistle registers, screams could easily reach 1000 hz, so their wavelength would be ${\frac {c}{f}}$, where c = 330 ms^-1 (speed of sound) and f = 1000 hz. So the wavelength of the screams would be about 34 centimetres (about 1 foot), and the length of each peak or trough would be 17 cm. It would look cool, but you probably wouldn't notice until you were fairly close to the wall (of course, men can scream in much lower registers, so if this happens to be close to the Hell mens room, the wavelength would be closer to 1 metre; much more dramatic). Of course, this all changes if your Hell is really hot or really cold; c is greatest in really hot conditions, so the wavelength would be much greater and more dramatic (and as a bonus, you'd get some very formidable looking Lavacicles forming). Laïka 09:08, 18 May 2007 (UTC)

May 17

Ducks

So, what's this duck? It's on a small lake in southern England, in a relatively rural setting. The same lake has a handful of common moorhens, at least one Eurasian coot, and the usual large collection of mallards. However, it's certainly not a mallard of any form, it doesn't look much like a coot or a coot chick, and juvenile moorhens are apparently not grey (plus it's quite large - I estimated it about the size of an adult one).

The legs are clearly like those of a moorhen, as is the body shape and beak, but the colouration (see also this) seems wrong. Any idea? Is this just a moorhen of unusual plumage? Shimgray | talk | 01:01, 17 May 2007 (UTC)

On consideration, I've only ever seen coot chicks in their "little bundle of fluff" stage, never really what they look like as "teenagers", as it were. Might this just be a reasonably old juvenile coot? I can't find any pictures beyond a comment saying "is paler"... Shimgray | talk | 01:10, 17 May 2007 (UTC)

I think it's a juvenile moorhen - the shape, stance, legs and bill colour all say moorhen. If it was a coot it'd have a dark undertail whereas this has a paler patch there; Collins Bird Guide also says a young coot should have a yellow-grey collar, which the young moorhen lacks. From the general dishevelled look, I suspect it's halfway between the dark grey downy stage and its paler juvenile plumage, which would explain why it doesn't have the white line around the edge of the wing yet. But IANBO. --YFB ¿ 01:38, 17 May 2007 (UTC)

Sounds fair. I have a recollection that whilst it was still on the bank it looked a lot more recognisably moorhen-like, but the camera wasn't properly focused at that point (as the image demonstrates, I was really rather pushing it anyway...) so I can't be sure. The thing that confuses me, though, is that there were three or four adult-plumaged moorhens around, some of which I swear were noticeably smaller than this. A male/female split, perhaps? Shimgray | talk | 17:46, 17 May 2007 (UTC)

Fructose being "better" in fruit than candy

My daughter often asks me sciencey questions at bedtime. Tonight, she asked me what the difference was between the sugar in sweets/candy and the sugar in fruit; I said "nothing, I think they're both fructose pretty much these days" (we're in the US). I asked her what made her wonder, and she told me another relative had told her that fructose that's actually in the fruit was "better" somehow; I said I'd go and ask them and get back to her. When I tracked the said relative down, they told me that HFCS is "refined" and therefore worse for you than "raw" sugar in the fruit. Is this true? I've looked at Sugar; what the relative called "raw" appears to be "natural sugars", and HFCS certainly isn't "refined sugar" as defined in that article, but I can't find anything that says that n grams of HFCS is worse for you than n grams of fructose (or even chemically different, other than whatever percentage of glucose it also contains). I stopped chemistry at GCSE, unfortunately. Can anyone give me a clue as to what to tell my daughter? Marnanel 01:43, 17 May 2007 (UTC)

The issue is complicated. In one sense the categories of "refined" vs "raw" are largely American cultural value categories like "clean" or "unclean" foods, except that the other components of fruit can slow the speed of consumption and digestion somewhat (reducing the rapdity of the effect on the blood glucose level-- i.e., the glycemic index), and may provide some additional nutritive value. In the 1970s, fructose was sometimes touted as a superior sweetener to sucrose because it also had a slightly slower impact on blood glucose levels. In the last decade, however, there is increasing suspicion that fructose (especially in the high fructose corn syrup form used in soda and many sweets) may have some unwanted attributes, such as a slower effect on hypothalamic satiety, or inhibition of insulin action in the liver, effects which may amplify either obesity risk or type 2 diabetes risks, respectively. Bottom line: fruit is likely better for her than anything containing high fructose corn syrup. alteripse 02:14, 17 May 2007 (UTC)

Fructose is much sweeter than glucose [reference needed]. Aaadddaaammm 02:49, 17 May 2007 (UTC)

Fructose is the sweetest of all sugars. http://www.answers.com/topic/fructose. According to the Fructose article on Wikipedia, the fructose in HFCS used to be glucose. some of the glucose was converted with enzymes into fructose.

Easiest way to have a self-sufficient life?

Well, I do like the idea of being green, but I also like the idea of being reliant on myself, so I was thinking about going (at least somewhat) self-sufficient. I figure the easiest way to do this without a huge lifestyle change would be to create a sturdy, economical, efficient, and eco-friendly house (i'm looking at a monolithic dome, which fits at least three of those), use natural power, and use all electrical appliances. That takes care of 99% of things, but I do have questions on that:

• Where in Canada would be the best place for a building like this? Preferably somewhere without a lot of building codes or permits needed, but still near towns or cities. I say Canada because there's always been a part of me that wants to leave the states, and it's the closest I could be to family, not to mention I have friends in Canada.
• In general, which is cheaper/more efficient, solar power or wind? Also, which is easier to maintain? Solar seems like it's less of a hassle, but then you have to have more batteries to power your house at night, and i'm not sure which is cheaper.
• Slightly off topic, but what electric car is the best mix of price, performance, and efficiency? By performance, I mainly mean how far it can drive on a charge. I'd probably have three vehicles, a small gas powered car for trips, such as something from japanoid.com, an Obvio, or a Smart, a small electric car for every day things like groceries, and an electric bike, for getting around town (driving to town in a car and parking and going around on a bike is a good way to not run out of fuel, I figure)
• Also off topic, but is it as much of a PITA to get odd/foreign cars street legal in canada? Japanoid.com makes me think it isn't, but it would be nice to know.
  

And then of course, to be more self-reliant, I'd have my own water and food supply. I figure gardening isn't too hard, and i'll probably still get most things from a supermarket, at least at first, but how would I handle water? I figure I'd need a well, is there any way to get this automagically? as in, have it made with the house, so it handles your water supply? And how would you purify it? I'm going to have a water purifier even for a government tap, I can't stand hard water, but I figure this makes it more complicated. Am I just being silly, and should I get a water line, since it would be impossible for me to be truly self-sufficient? thanks for reading all this, -- Phoeba Wright^OBJECTION! 02:11, 17 May 2007 (UTC)

Would your ethics allow you to just buy a house with existing well and septic tank ? Many exist in isolated rural areas, which are losing population, so they should be available cheap. StuRat 02:20, 17 May 2007 (UTC)

It's not really about ethics, more about just being able to live by myself without making a huge impact on the enviroment. That's probably a good idea, but I don't know how easy either of those are to use (mainly, how to maintain a septic tank, and how to get a water supply for your house out of a well), and I want to make a monolithic dome home (see monolithic.com). I have extremely messed up ethics, they aren't a concern for me -- Phoeba Wright^OBJECTION! 02:41, 17 May 2007 (UTC)

Electric bike? What about a traditional bike? Also, I have my doubts that an electric car + electricity + all the infrastructure you're going to need to keep it charged + a spare gas powered car for trips is more economical than just having a gas powered car, and electric car batteries are extremely difficult to dispose of in an eco-friendly manner. I don't think it's that big of a deal to dig a well. --froth^t 03:51, 17 May 2007 (UTC)

Comment - Self-reliance and environmentalism are separate ideas, and often even mutually exclusive. Nimur 04:26, 17 May 2007 (UTC)

Very True. Anyway, I was thinking a spare car would probably be something old, but still fairly cheap, like the ones I listed. I didn't think digging a well would be a big deal, it was using one to run a house (dishwasher, laundry machine, shower) and having pure water from it, and septic system maintenence. A traditional bike would work, but an electric assist is never a bad idea to have when you're tired. The infrastructure would mainly be for the house, not the car, I don't get out much, so I doubt an electric car would be sucking very much juice. I've also wondered, in Canada, if you hook your house up to the power grid, but generate all your own power, are they required to pay you for the electricity you're pumping back into the grid? I'm fairly sure they are in most parts of the US, but it would be nice to know if it works elsewhere. -- Phoeba Wright^OBJECTION! 07:28, 17 May 2007 (UTC)

I think winnipeg has the "windiest corner in North America" [17] so, if you built there, I think wind power might prove effective. Edmonton is also high ranking in terms of hours of sunshine if you'd rather go the solar route, but land around that city's crazy expensive.

Hovering Shoes

Above there is a thread about "shoes/skis" that float on water...what about ones that work on land? They would essentially be frictionless, or floating a few inches off any ground. Lean in the direction you want to go, and a sensation similar to running and sliding on a patch of ice would occur, moving you long distances with little effort. How would this be accomplished technologically? 140.180.11.227 03:03, 17 May 2007 (UTC)

With great difficulty. You could probably achieve that effect with high-pressure air or some sort of jet propulsion, but it would be very heavy, consume a great deal of energy and probably be difficult to control. Get a Segway. --YFB ¿ 03:24, 17 May 2007 (UTC)

Fill them with vacuum such that they displace a weight of air equal to that of the person plus accouterments. Eldereft 05:00, 17 May 2007 (UTC)

They'd need a volume of somewhere approaching 50m^3 for a 60kg person. Not very practical? Capuchin 12:00, 17 May 2007 (UTC)

50 cubic meter shoes would need a surface area around 60 square meters - with air pressure at around 10 tons per square meter - the shoes would have to be able to withstand 600 tons of pressure. We're talking heavy steel structures here! Oh - but wait - isn't steel rather heavy? You are much better off filling them with helium or something. "Vacuum balloons" sound like a great idea - but you can't make them strong enough to resist air pressure. SteveBaker 13:12, 17 May 2007 (UTC)

Rollerblades? "Heelys" (my son had those - they were very cool!) They are pretty close to frictionless. I don't see how 'leaning in the direction you want to go' helps though. Wheels work well because they offer little rolling resistance in one direction - yet you can push sideways on the shoe to get some thrust to get you moving. Totally frictionless shoes would be impossible to walk in. SteveBaker 13:17, 17 May 2007 (UTC)

You could hold a lot of helium baloons, and therefore reduce the force pulling you toward the ground. This would reduce friction a lot. If you had enough balloons

Black holes again!

If you're falling feet first into a black hole and you're past the event horizon, could you look down and see your feet? Or would it be a slightly delayed image of your feet (until your eyes could overtake the light rays)? How far could you see down into the black hole? Could you even see the singluarity, or would your eyes actually have to be on it to see it? It's a very large one, so you don't have to worry about spaghettification :) --froth^t 03:40, 17 May 2007 (UTC)

Surely something would kill you before you would be able to recognize it. Are you asking whether light could travel radially outward from the singularity towards the eyes, which are closer to the event horizon? Probably not, since it is gravitationally captured by then. More to the point, even if any light could travel back outward (even if it never re-crosses the event horizon boundary), the amount of distortion of the rays would preclude image formation. Nimur 04:16, 17 May 2007 (UTC)

This is how I think it must work (somebody more knowledgeable please correct me if I'm getting it wrong): Yes, you would see your feet. The photons leaving your feet "trying" to head outward would actually fall backwards toward the center, but your eyes would be falling faster and would catch up with the photons. However, the image you would be seeing at any one moment would depict an event (the moment when the photons left your feet) that occurred when the feet were located further away from the center than your eye is when you see the event. Same thing with your unfortunate friends who fell in immediately before you: you might see them, but only as they were at a time when they were not yet as far in as you are when you see the image. Thus you are, in a strange sense, not really looking "in" toward the singularity, but back outward. In particular, you could not "see the singularity". In fact, I think what you would see at the furthest apparent distance in front of you would be a (very darkened, for all practical purposes invisible) image of events that happened at the event horizon behind you a long time ago. For you, however, in your local reference frame, everything would feel rather like normal... for a while, until the tidal forces would start to rip you apart. --mglg_(talk) 04:33, 17 May 2007 (UTC)

Looking at the same thing in a totally different way: once you are inside the event horizon, your local spacetime coordinate system has been rotated so that all positions (events) that lie closer than you to the center (spatially closer according to the coordinate system of a distant observer) are in the future for you. (More precisely, your whole past light cone lies outside of you.) You cannot see events that lie closer than you to the center, for fundamentally the same reasons we cannot see into the future in everyday life either. But, again, from your perspective your local spacetime is perfectly normal, and you don't feel anything funny (yet). --mglg_(talk) 04:50, 17 May 2007 (UTC)

It may be enlightening to think about the moment when your eyes pass the event horizon. Any light that was ever emitted straight outward exactly at the event horizon will remain hovering at the horizon forever, eternally trying to escape. And that is all the straight-outward-directed light that will be there: light emitted outward from outside the horizon will escape, and light emitted from inside the horizon will fall inward. Therefore all the events that you see, when your eye is at the horizon and you are looking straight inward, actually happened at the same spatial point, namely that point on the event horizon where you are, but at different times (all according to the distant observer's coordinate system). Recent events will look close, and early events will appear to be further away. But to you it will look normal; according to your local (co-moving) coordinates, the events that look like they are located toward the center from you actually are. The difference of opinion between you and the distant observer is not all that different from a "normal" Lorentz transformation between the coordinates of different reference frames that move relative to one another, as encountered in special relativity. --mglg_(talk) 16:03, 17 May 2007 (UTC)

Biochemistry Universities

In your opinions, what are the leading universities in the world in terms of biochemistry research? Aaadddaaammm 04:05, 17 May 2007 (UTC)

This is a very tough thing to answer because biochemistry is such an immense field. You could start with silly and useless comparisons of research-dollars, number of faculty, and other "marker" statistics, but you should think about narrowing your focus. Any top research university will certainly have a strong biochemistry program, with specialization in some areas. Nimur 04:09, 17 May 2007 (UTC)

Addendum - However, if I had to name favorites, I would pick any university with a good balance between work and aesthetics. Good science is everywhere; good weather is not. Nimur 04:11, 17 May 2007 (UTC)

I sincerely doubt that cutting edge biochemistry research is found at every college where there is a balance between work and aesthetics. [18] lists the top biochem grad programs in terms of NIH research grants, and [19] is U.S. News list of a variety of schools with biochem undergrad programs. Although they list the ranking of each, I did not see a way to sort by the ranking of the biochem program. If an undergrad, you might consider the overall quality of the school, its location, its costs, etc. Edison 13:47, 17 May 2007 (UTC)

Edison, my comments were meant to illustrate the fallacy in a total order ranking of "merits" or "cutting-edge-ness." Cutting edge in industrial applications is very different from cutting-edge academics; and funding dollars are only one way to gauge the performance and quality of work. I believe it is more advantageous to consider the quality of a specific sub-discipline, if a student is pursuing research work. Nimur 21:09, 17 May 2007 (UTC)

McGill -Arch dude 02:58, 18 May 2007 (UTC)

Random v. linear evasion

A few years ago, I recall reading, or possibly hearing in a lecture, that some species of rodent (?) had shifted its behavior due to collision with cars. This species previously ran in a randomly shifting path, but generally in a line. This strategy worked well for evading predators, but not so much for cars. In recent times, repreated collisions with cars had selected for a more linear evasion path. My question, does anyone have more information on this, possibly even a species or (blessed be) a citation? Many thanks, --TeaDrinker 04:49, 17 May 2007 (UTC)

The closest thing I can find in relation to this topic is the effect of fencing along roadways, which can create geographic separation of the population, leading to evolution and eventual speciation. I tried this google scholar search which resulted in mostly unrelated biochemistry subjects. Maybe you can further refine it? Nimur 05:31, 17 May 2007 (UTC)

I've been told (no RS, unfortunately) that this is because it's easier for drivers to predict the path of something moving with constant speed and direction (velocity), as opposed to something that's randomly jerking around. I've also heard this is the best way to avoid getting run over if you feel you must cross against traffic, but I would not recommend testing this. Someguy1221 09:42, 17 May 2007 (UTC)

the presence of melanin(pigment) in human skin is determined by human gene . presence of melanin makes skin look darker .

it is seen that when a person exposes his skin long time under sunlight his skin becimes darker . my question is how is this possible while his gene remains the same ? is this process reversible ? what can one do to regain the skin colour that he had while he born ?

I believe it is because the sun's rays cause the person's skin to produce more pigment, although that's not a very precise answer. I think if you just avoid sunlight for awhile, tans will go away, in slightly more extreme terms, you could try skin bleaching or other cosmetic surgery -- Phoeba Wright^OBJECTION! 07:46, 17 May 2007 (UTC)

When human skin is exposed to sunlight (in particular, Ultraviolet radiation) a pigment called "melanin" is released that makes the skin darker. Melanin comes from cells called Melanocytes. Differences in genes, however, affect the activity of these cells. So a person who, without the effect of the sun, has darker skin is likely to possess melanocytes that are more active than someone who has naturally light skin. I would say that after exposure to the UV radiation has ceased the melanin may begin to break up and disappear. More information can be found at Sun tanning. Vvitor 07:52, 17 May 2007 (UTC)

Great question, and the very good answers above lead to a couple of braoder ideas that might interest you: The physical characteristics (phenotype) of a person (or any living thing) are affected by both their genes (genotype) and their natural environment, which includes things like diet, lifestyle, and in this case, exposure to the sun. The perfect human would have skin that would darken and lighten instantaneously in response to their environment, because although too much sun causes cancer, some is still required for vitamin D production, so a happy medium is needed. This is homeostasis. We haven't evolved to travel to different continents on holiday, so our genes give our skin just enough plasticity to cope with the changing seasons, which is why we need sunscreen to supplement our skin's natural protection when travelling to places sunnier than our ancestral lands. You may have noticed that equatorial Africans don't get lighter living in Scandinavia; this is because there are no seasons on the equator so have little evolved plasticity! Bendž|Ť 14:42, 17 May 2007 (UTC)

Well, you seem to be puzzeled that it's in the genes but depends on sunlight. Have a look at Regulation of gene expression. 84.160.208.134 18:29, 17 May 2007 (UTC)

Conservation of Mass - kids

By what age do children develop an understanding of conservation of mass?— Preceding unsigned comment added by 122.169.10.154 (talk • contribs)

When they can feed themselves and use the lavatory unassisted.--Shantavira 13:24, 17 May 2007 (UTC)

The Theory of cognitive development of Jean Piaget (1896-1980) says that children go through a series of stages, although not all at the same age. In the third of these, the Concrete operational stage, at about age 7 to 11, they develop notions of reversibility (things can change shape and return) and conservation. Anecdotally, I remember when I was younger than this, an older child who was sharing a bottle of Coca Cola with me would offer me a choice of a thin tall glass or a short wide glass, and it really looked like there was more in the tall glass, but I knew from his smile that there was a trick to the process. Similarly, a child before this stage will think there is really more clay when modelling clay is rolled out thin. Of course there are also post-Piaget theorists. Edison 13:31, 17 May 2007 (UTC)

Acidity of "Special Parts"

Dear Wikipedians,

Wat is the acidity of a human vagina?

The normal vaginal pH is 3.8 to 4.5. --BenBurch 15:52, 17 May 2007 (UTC)

Lightning

What would happen if a nuke was hit by lightning in mid flight?

It might short out the detonation circuits so the bomb wouldn't go off, or screw up the onboard navigation technology, but it's extremely unlikely that the strike would detonate it. Anchoress 15:53, 17 May 2007 (UTC)

Disclaimer - Under carefully controlled conditions, Lightning does whatever it feels like doing... However Apollo 12 I think it was was hit by lightning shortly after lift off and survived. Nuclear weapons are designed to withstand EMP from nearby nuclear detonations, and so I would expect lightning to have little effect. However, it might kill the bird at which time it would most likely fall inert. --BenBurch 15:57, 17 May 2007 (UTC)

lightning is trying to find the easiest way to the ground, so I doubt it would hit a flying object, even if it is much higher than any trees/buildings around it :) HS7 17:28, 17 May 2007 (UTC)

It is not at all uncommon for lightning to strike an airplane in flight. There is a potential difference between an uncharged metal airplane and a charged cloud. If it is large enough, the air will become ionized and voila a lightning strike. On May 8, 1996, Illinois Governor Jim Edgar's plane, a Beechcraft King, was struck by lightning while in flight, per [20] and he lived to tell about it. It started a small fire inside. No ground wire necessary. Edison 20:42, 17 May 2007 (UTC)

Actually I think it is highly likely that if lightning strikes nearby that it will hit a falling bomb, since the metal of the bomb would offer much less resistance then the equivalent amount of air the lightning would have to travel if it didn't hit the bomb. But as above, I don't think lightning would do anything to a nuke, like a plane, the lightning would just pass through. Vespine 22:46, 17 May 2007 (UTC)

Have you not seen the holes in aircraft lightning can cause? (See [21]) Yes, most likely no effect, but there is more energy in a stroke than you can easily imagine. --BenBurch 05:15, 18 May 2007 (UTC)

Marx generator?

Can I make a functional marx generator with only a 35 volt DC power source? Or is that voltage too low to make a working spark gap?

If you run the DC through a vibrator and the resulting pulsed DC through a transformer to step up the voltage, you can likely make it work. --BenBurch 16:02, 17 May 2007 (UTC)

To get a spark in air you need a field strength of about 3 kV/mm, see electrical breakdown, so for any reasonable gap spacing you would need very much higher voltages than 35 V. There are ways to create such voltages, but please do not do this. High voltage backed by significant capacitance is an excellent means of getting yourself killed quick. --mglg_(talk) 17:26, 17 May 2007 (UTC)

Agreed, but there are ways to work with this safely. I mean, I'm still here after 40 years of electrical tinkering. You just have to learn the safety precautions to take and never, ever fail to take them. --BenBurch 17:29, 17 May 2007 (UTC)

OK, if you do know what you are doing, see DC-DC converter. You can buy ones that put out 6kV. Some of these actually work much the same way as the Marx generator, on a smaller scale, with FETs instead of the spark gaps. You could use one to charge your Marx generator with, or hand-build a long one instead of the Marx--169.230.94.28 20:25, 17 May 2007 (UTC)

Use of Jasmine and Rose flowers

Kindly let me know the method of pollination in the above two flowers(Jasmine and Rose). Please tell me if in these plants seeds are produced? Where are thwe seeds found? Can new plants be grown from these seeds? Are these seeds sold? 202.71.137.235 16:12, 17 May 2007 (UTC)Hemchandra

You can in fact grow roses from seed, see [22]. Most often it is done by cuttings though so as to preserve particular traits that would likely be lost in sexual reproduction. --BenBurch 16:52, 17 May 2007 (UTC)

The rose seeds are found inside fruits known as rose hips. --mglg_(talk) 21:10, 17 May 2007 (UTC)

Ashwagandha

Please tell me are Ashwagandha leaves used for weight loss? And please tell me the different types of Ashwagandha plants?

Ashwagandha#Medicinal use doesn't seem to mention weight loss specifically. Algebraist 16:33, 17 May 2007 (UTC)

(after edit conflict) Ashwagandha = Withania somnifera. Seems to be used a lot in traditional medicine, but I could not find any indications in literature that it induces weight loss. In fact, this reference [23] (which deals with carcinogenegis ihibition in lab mice) specifically states that the mice did not lose weight when fed Withania somnifera. Most important, we do not give any medical advice!. No, really, we don't. And, ingesting medicinal plants without consulting a certified physician first is a really, really bad idea. Take care. Best regards, Dr_Dima.

To amplify, there are very few medicinal plants that can be safely used as a medicine. This is because the medicinal effect depends on the amount of whatever active ingredient is in the plant and this can vary greatly. Most medicinal plants have a toxic dose level, and often this isn't far from the clinical dose level. In addition medicinal herbs can pick up traces from the soil of heavy metals and herbicides and other things that are simply no good for you. Unless we are talking about something very safe like Camomile tea or eating Marijuana, I'd stay away from herbal medicines entirely. --BenBurch 16:58, 17 May 2007 (UTC)

Ramdev baba(Yoga teacher) says that when the leaves of this plant are consumed weight is lost but when thw churan(powder)of this plant is eaten weight is gained. Is it True?

blood system

how long does morphine stay in blood system?

Until it's gone

Our morphine article says it has a half-life of 2-3 hours, so its concentration in your blood stream halves every 2-3 hours. (Be sure to also see Biological half-life.) In theory, it's never actually gone, but in practice, by 10 half-lives later, it's down to 0.1% of its original concentration and so is certainly no longer clinically effective. But if the question is really "how long till one can pass a drug test?", that's probably a lot longer, depending on the sensitivity of the drug test and which metabolytes it's looking for.

Atlant 17:24, 17 May 2007 (UTC)

Torch testing In Software Jargon

hi, recently i came across torch testing, wud really be helpful if anyone cud explain what is torch testing in software testing scenario??

Sounds similar to a smoke test. DMacks 18:20, 17 May 2007 (UTC)

OK this really is the final starch question

So I have basically decided there are clearly no quantitative tests for starch. You could have told me a few weeks ago then I wouldn't have wasted my time. But nevermind. I still need to test for starch quantitatively, but it appears I will have to use iodine to do it. So, are there any ways that I can do something to the iodene so that it only reacts a little bit to the starch, so that I can see how much starch there is by how much or how quickly the iodine changes, without it all going dark blue as soon as it gets near any starch? I really need help here and as soon as possible.

A little bit of starch makes a lot of darkness with iodine, and it's a fairly fast and complete reaction. If you want gradations visible to the naked eye, your best bet would be to use very small or dilute samples. DMacks 17:11, 17 May 2007 (UTC)

Small samples of starch? I don't think I can do that. Basically I have a leaf, and I need to know how much starch there is in it at a specific time.

Would cutting a very small bit off of the leaf, and only testing that for starch help :) I really wouldn't know as I am not a very good scientist, (as any regulars here will tell you) :( HS7 17:19, 17 May 2007 (UTC)

I think something like (testing a small cutting instead of a whole attached leaf) that would have to done anyway...I think the iodine test is a destructive test on the sample. DMacks 17:31, 17 May 2007 (UTC)

I do have lots of leaves I can test if each one gets damaged. How small would it have to be for the starch to not change totally?

I am going to go with cutting a very small bit off. Someone tell me quickly if this is wrong.

I have no idea "how much" of the things you'll need here to get a good visual gradation. I guess that's why they call it an experiment. DMacks 18:04, 17 May 2007 (UTC)

One final last thing would I be able to test for starch without boiling the leaf for a few minutes first? Would it continue photosinthesizing during this time? How long will it take to prepare a leaf for the test?

A few minutes is unlikely to make a huge difference in your detection data...since you're looking for (I assume) differences among different leaves, you'll still see the same differences as long as you are consistent in your timing and preparation process. A few minutes probably won't affect the data that much; if you're concerned about having photosynthesis stop at a precise time (vs continuing during the prep), do the prep in the dark (or very dim light) and get the leaf into very hot water very quickly (destroy the biological starch making and using processes). DMacks 18:18, 17 May 2007 (UTC)

This might well be totally wrong, but could you test the leaf without boiling it, therefore making it difficult for the iodine to get into the leaf, and thereby making the test take longer :? Would the Iodine acyually be able to enter the leaf through stomata and the cut edge :) HS7 18:21, 17 May 2007 (UTC)

Does a thermodynamic capacitor exist?

Can anyone explain me The mechanism by which could a capacitor absorb sunlight-generated heat and convert it to electricity? JammieJammiefungt 17:47, 17 May 2007 (UTC)

I don't think capacitor is the name for such a thing. Maybe solar panel or Solar cell would help? Friday (talk) 17:49, 17 May 2007 (UTC)

Of course you could always connect a regular capacitor to a solar cell

Have a look at Thermoelectric effect 84.160.231.206 18:41, 17 May 2007 (UTC)

So a thermodynamic capacitor does not exist....

Ok. Is there nothing pther than solar panels? A Thermo-Transducer or something simpler as to not make-up words?

If you're asking about devices that convert solar energy into electricity, there's no need to invent new names for them. See solar cell for a large informative-looking encyclopedia article on this topic. Friday (talk) 18:19, 17 May 2007 (UTC)

The thermoelectric effect was already linked for you. As far as devices that convert electromagnetic energy from the sun into useful energy for humans go, three main options come to mind: photoelectric (quantum) effects (optical to electrical direct conversion), purely thermal effects like the aforementioned thermoelectric effect and things like solar water heating (this covers a broad range of devices), and chemical (such as the useful chemical energy plants store just for your consumption). -- mattb 22:51, 17 May 2007 (UTC)

Can a lake have two outlets?

Can a lake have two outlets? So that it creates an island in between? Why or why not? --Spoon! 19:10, 17 May 2007 (UTC)

If you want to create an island - yes. It is not uncommon. A mound of earth forms in a single outlet, trapping sediment, and grows. The two outlets go around the mound and rejoin. This also happend right in the middle of rivers (I can see one from my office window - it is called Drum Island, a little island in the middle of the Cooper River). As for two outlets that do not create an island between them, that is also possible, but less common. High altitude lakes can form more than one outlet river and the rivers do not have to join together downstream. --Kainaw ^(talk) 19:17, 17 May 2007 (UTC)

Of course assuming the rivers end up in the sea and don't flow through tunnels and you define an island as a peice of land surrounded by water than two outlets have to create an island it just might be a rather big one ;) Plugwash 19:20, 17 May 2007 (UTC)

If you do a Google search on "lake" and "two outlets", you will find many examples. The first hit that's in Wikipedia is Highland Lake (Stoddard, New Hampshire). Of course, when a lake is artifically made or its flow is controlled by dams, it has as many outlets as the dam engineers want. A notable example is Gatun Lake in middle of the Panama Canal, which supplies water to both parts of the canal. --Anonymous, May 17, 2007, 22:57 (UTC).

• Lake Michigan has two outlets. The Chicago River was reversed many years ago and now flows out of the lake rather than into it. --BenBurch 23:58, 17 May 2007 (UTC)

Flower identification

I posted this a few weeks ago without success in identifying it. I had suggestions of foxglove, snapdragon, and Texas Bluebonnet, none of which quite seems to match. Can someone help identify it? J Are you green? 20:35, 17 May 2007 (UTC)

Could you give us some more information, such as on what continent and in what environment the flower was found , whether it grew wild there or might have been planted, etc.? --169.230.94.28 20:44, 17 May 2007 (UTC)

From afar it looks like one of the many, many variants of Impatiens. Could be tricky to find the right one and verify it. 84.160.231.206 20:53, 17 May 2007 (UTC)

I'm almost certain it was not wild. It was in a garden in mid-eastern United States. J Are you green? 21:03, 17 May 2007 (UTC)

Penstemon?

Relative Speed

If an object is going at or close to the speed of light and another object is going in the opposite direction at the same speed.

Wouldn't the second object be going faster than the speed of light relative to the first object or vice versa? --M.A.D.M.D. 21:49, 17 May 2007 (UTC)

See velocity addition formula. Short answer: no. --Tardis 22:17, 17 May 2007 (UTC)

It actually depends on in whose frame of reference you are interested. If you stand next to the railroad and observe two trains going by in opposite directions, each with a speed close to $c$ (in your frame of reference), then yes, their relative speed is greater than $c$, as far as you are concerned. But for an observer on one of the trains, the other train does not have a speed greater than $c$ relative to the train with the observer. The rule is that whenever you measure the speed of an object, you will find that it moves with a speed less than $c$ relative to you, the observer. —Bromskloss 23:18, 17 May 2007 (UTC)

That's a fair point, but the trick is to define "velocity relative to". When considering just two objects, it's somewhat odd to define the velocity of one relative to the other as being the simple subtraction of their velocities as measured by an third party (because it depends on which third party!); of course, M.A.D.M.D. implicitly introduced that third by giving both objects a velocity to begin with. It still strikes me as more fundamental to take "relative to" to mean "as measured in the frame of", even though in this case that's largely discarding part of the question, at which point my simple answer applies. --Tardis 15:45, 18 May 2007 (UTC)

100% reflextion

is there a material that reflect 100% light and absorbs nothing from it ?

Every material has a critical angle at which it reflects all of the light. --M.A.D.M.D. 22:12, 17 May 2007 (UTC)

The best we've got is dielectric mirrors. The percentage of light reflected and not absorbed has a lot of nines in it. [Mac Δαvιs] ❖ 22:32, 17 May 2007 (UTC)

Note that these very high reflectivity mirrors are typically fairly narrow-band. See distributed Bragg reflector. Incidentally, I have to disagree that light incident beyond a critical angle will experience truly total reflection. Some small amount will still be lost, just as the second sentence of that article hints at. -- mattb 22:43, 17 May 2007 (UTC)

Sure: see Unobtainium. -Arch dude 02:31, 18 May 2007 (UTC)

mouse

what would a mouses nipples look like if its suckeling babys because ive never seen what a mouses nipples look like normal compaerd to a mouse that isnt suckleing young i would rather have a image thank u for your time --Sivad4991 23:00, 17 May 2007 (UTC)

I didn't have much luck, but did find this site showing the diff between male mouse nipples and female mouse nipples (near bottom of page): [24]. It seems to imply that, as adults, you won't be able to see the nipples unless the female mouse is nursing. StuRat 05:18, 18 May 2007 (UTC)

May 18

heat to elrctricity

what is the best known way to transfer heat to electricity?

A steam turbine driving an electric generator. Those articles should help you out. 161.222.160.8 02:16, 18 May 2007 (UTC)

How much heat? At what temperature? How much electricity? how do you define "best"? in some situations, the aforementioned turbine/generator is best. in other situations a thermocouple is best. There are a very large number of alternatives depending on the particular conditions. -Arch dude 02:28, 18 May 2007 (UTC)

thermocouple are used to mesure heat but can it be used to make large quantity of electricity? and how afficient are steam powered turbines in % of convertion?

also ive been wondering if surounding a container with a heat source in it with aerogel would keep all the heat inside or if it would absorb it?

"All" and other such superlatives are usually tricky words in the engineering world. Aerogels are extremely good insulators, but not perfect ones. There's always some non-ideality that makes "all" untrue. As Arch dude pointed out, scale has a LOT to do with efficiency. Schemes that are fairly efficient on a large scale (like the steam turbine) are often very ineffective at smaller scales (such as micro power generation for MEMS and self-powered ICs) and vice versa. There's rarely a "best" solution to any problem, especially one so broadly phrased. -- mattb 04:16, 18 May 2007 (UTC)

what would you propose for extremely high heat , im trying to think of the best way to turn to electricity a solar furnace and im trying to figure out if there would be a way to achieve higer % of energy convertion or more cost eficient way to turn sunlight to heat

How high, like thousands of degrees (using mirrors to focus light on a small volume) ? A steam turbine would still work if you have a nice free supply of water, like a river. If you need to reuse the fluid, perhaps instead of water you should use some fluid with a higher boiling point. StuRat 05:04, 18 May 2007 (UTC)

You also need to define your goals a bit more precisely. Do you want to produce the maximum amount of electricity per dollar of install price, per dollar over the projected life of the solar collector, per square foot of surface area, etc. ? These different cases may lead to using very different technologies. Your choice would also depend on the sunlight patterns in each particular location and other factors like tax incentives. Also, if you need to supply energy when the Sun is down, this necessitates more expensive equipment. StuRat 05:04, 18 May 2007 (UTC)

Price of chemical type stuff and stuff

Where can I find the prices for stuff like liquid nitrogen or uranium or potassium permanganate or sodium chloride? Also, where can I buy this stuff? Thanks.--71.175.125.135 02:17, 18 May 2007 (UTC)

Well, liquid nitrogen probably requires a permit of some kind, but once that's covered I'm told it's cheaper than milk by volume (and with the price of milk these days I'm not surprised). Potassium permanganate is, according to the article, available over the counter from pharmacies in the former Soviet Union, and I suspect would be available from maybe hardware stores. Sodium chloride ... ARE YOU MAD?!?!? That stuff's as dangerous as DHMO!

But in general, if you were looking for high quality, pure supplies of chemicals in general, ie. suitable for lab work, and especially if you were looking to buy in bulk, there seem to be a lot of companies selling this kind of stuff according to a quick Google search. You'd probably also want to check the Yellow Pages (or local equivalent) for "Chemical supplies". A good supplier would, I believe, take fairly heavy steps to make sure that you're aware of any safety issues involved, and also keep a track of what you were buying to make sure there was no nefarious purpose involved. Confusing Manifestation 02:29, 18 May 2007 (UTC)

I don't believe liquid nitrogen requires a permit, and is indeed fairly inexpensive. However, the containers to store it in can get pretty expensive, depending on how much you want to store. I seem to remember a previous discussion here saying that a normal thermos wouldn't work for storage. --Bennybp 02:54, 18 May 2007 (UTC)

Thanks guys. Is there any website that I could look at that would list prices for stuff like this?--71.175.125.135 03:05, 18 May 2007 (UTC)

By the way, you didn't mention uranium. :) --71.175.125.135 03:05, 18 May 2007 (UTC)

Well, like I said, the Google search brings up a large list of suppliers. Just going to the first one, http://www.alfa.com, you can search their catalogue and get prices. For example, 99.99% pure NaCl will cost you about $40/50g, or $150/250g (and apparently you can get a quote for a bulk order, presumably giving you a discount). Which is quite an expensive way to flavour your food ;) They also have some KMnO4 in stock, but no LN2 or U - you'd probably have to look elsewhere for them (perhaps a more specific Google search, although I'd point out that amassing quantities of radioactive substances can get you into trouble sometimes, as David Hahn would attest). Confusing Manifestation 04:29, 18 May 2007 (UTC)

You should also be aware that there is a hidden cost to chemicals: disposal. When it comes time to get rid of whatever you have, many if not most lab chemicals can not be poured down the drain or buried in your back yard. Be sure to ask your chemical supplier and/or hazardous waste disposal outfit where and how you can rid yourself of the stuff (or anything you make with it). You may have paid for it, but you may have to pay even more to get rid of it. --TeaDrinker 06:24, 18 May 2007 (UTC)

http://unitednuclear.com/ has some pretty cool stuff for sale. 69.244.213.58 17:26, 18 May 2007 (UTC)

Can Elephants Really Paint?

I know they can hold a brush and can be interested in smearing a canvas with paint, but can they see color? Do you guys know of any study where it's shown that elephants can appreciate color and lines? Because if they can, then that would mean that their paintings can be an expression of what they think or whatever is going on in their head. Moonwalkerwiz 02:53, 18 May 2007 (UTC)

Most mammals have dichromatic color vision: they see color but not as well as us trichromatic primates. This includes elephants, as I found out with a simple Google search on "elephant", "color", and "vision". Whether elephants are capable of forming the concept that marks on paper can represent the appearance of something, I don't know. --Anonymous, May 18, 03:07 (UTC).

Thanks. So at least I know now that they see the colors they paint differently than people see them.Moonwalkerwiz 03:53, 18 May 2007 (UTC)

There have been color blind human painters. Anyway, who says appreciation of color and lines is required to "paint".. or even to produce "art", whatever "art" is. It may be that elephants don't understand their paintings very well, but then, I'm skeptical that human painters actually have a halfway decent understanding of their own work. Pfly 03:09, 18 May 2007 (UTC)

I know that. I'm not talking about the author's death here. Anything can be art if we're talking about perspective. But it's different if elephants can actually associate something in colors and lines. Like, if they know they paint orange, that they like orange, or if they paint the orange horizontally, it's better than if they paint it vertically.Because if they could, then their work is not merely accidental, but has some degree of intention in it. That means that if you bought an elephant painting, that the elephant, in some degree, however small, intended the painting to be that way. Moonwalkerwiz 03:53, 18 May 2007 (UTC)

I'm sure elephants make paintings which you'll never forget. 04:50, 18 May 2007 (UTC)

is there any secure website where anyone can submit their new scientific idea for worldwide response having all the rights of the invention ?

ur answer should include external links .

If you can demonstrate the idea and it is fairly novel, peer reviewed journals might be an option. What kind of response in particular are you looking for? In most countries you must apply for a patent (I assume this is what you are getting at) before public disclosure. The U.S. is an exception, in which you may still apply for a patent up to a year after you disclose the idea. -- mattb 04:26, 18 May 2007 (UTC)

Halfbakery, although if you don't have a patent, I doubt anything will protect you -- Phoeba Wright^OBJECTION! 04:35, 18 May 2007 (UTC)

Electrical Current

Hello. In a series circuit with multiple loads, does the current stay the same? Thanks. --Mayfare 03:45, 18 May 2007 (UTC)

See charge conservation. Basically, yes, assuming that there are no other paths for current to flow out of the circuit (that is, the components are truly in series). -- mattb 04:22, 18 May 2007 (UTC)

Are you talking about AC or DC circuit? If you measure the instantaneous current in an AC circuit, you will find that the current goes up and down, positive and negative as times goes on. Hence the term Alternate Current or AC. 202.168.50.40 04:33, 18 May 2007 (UTC)

Egg yolks

In egg yolk:

The yolk makes up about 33% of the liquid weight of the egg;

Which one has more yolk by weight? A small egg or a large egg? -- Toytoy 03:53, 18 May 2007 (UTC)

Well, unless this is a trick question, 33% of a large egg would weigh more then 33% of a small egg, right? Vespine 04:22, 18 May 2007 (UTC)

Shouldn't that be 33% of the mass of the egg? The use of "liquid weight" rather than "solid weight" suggests that some sort of weight transference takes place upon cooking, which I don't imagine it does.--Shantavira 07:09, 18 May 2007 (UTC)

Is it not just discounting the mass of the shell? And I would assume it was talking about an uncooked egg; the percent could be different in a cooked egg, I suppose. Skittle 10:07, 18 May 2007 (UTC)

Liquid weight vs. the shell weight perhaps? Dismas|^(talk) 10:12, 18 May 2007 (UTC)

Left shoe squeaking more than right

I have noticed that my left shoe squeaks more than the right. Now that I think of it, the last 3 pairs of shoes I have bought (different brands, medium prize) started squeaking on the left shoe before the right. It seems I am not the only one who have noticed this phenomenon: http://www.cs.utexas.edu/~arao/writings/squeaky.html

I think my feet are pretty much the same size, and I don't think that I often go counterclockwise around in circles.

"Coincidence is God's way of remaining anonymous" -A. Einstein

130.225.96.2 09:20, 18 May 2007 (UTC)

Not sure whether there is a question in there, or a request for a straw poll, but "left shoe squeaks" gets about the same number of G-hits as "right shoe squeaks", and I can't think of any reason why one shoe should sqeak more than another, although since most people lead with their right foot, the forces applied to each shoe might be differently distributed...--Shantavira 10:10, 18 May 2007 (UTC)

If it were random chance, the odds of three pairs of shoes starting to squeak with the same foot is only one in four - it seems likely that it's just chance at this point. SteveBaker 11:02, 18 May 2007 (UTC)

Maybe it's not the shoes that are squeaking ;) 213.48.15.234 11:18, 18 May 2007 (UTC)

using various nimh batteries togather

hi, I sometimes charge and use 2 AA batteries that have different currents (600mah and 1800 mah ). Will this damage the charger or the device (pocket radio)?. The charger is a wall socket type that could charge a maximum of 4 batteries, 2 on the top side and 2 on the other side (please look at www.onlybatteries.com/webimages/images/10965.jpg). I read that one must charge either 2 or 4 batteries at a time but not 1 or 3 batteries as this will damage the charger. Is this true?. Please pardon my bad english.

131.220.149.185 10:37, 18 May 2007 (UTC) charger

Yes, it could catch fire, and yes, you should always charge batteries in matched pairs. 213.48.15.234 11:14, 18 May 2007 (UTC)

Mineral Hardness

I am doing a bible study on Rev. 21: 9-27, in this scripture a wall of new Jerusalem is described. The wall consist of twelve stones, as follows:

Jasper Sapphire Chalcedony emerald sardonyx sardius chrysolyte beryl topaz chrysoprasus jacinth amethyst

I am trying to find the hardnes of each stone to show the strength of this wall in Heaven. I have found some of the comparison charts showing the stones in relation to other stones but not the hardness, or how many pounds before stone will collapase or be crushed. Can you give me direction to where to search or a scale that reveals all the stones.

Monty

Um, that's an unusual way of reading the Scriptures. Don't you think you are missing out on the real message of it? —Bromskloss 11:19, 18 May 2007 (UTC)

Hardness is very hard to quantify. The Mohs scale of mineral hardness is a good start. 213.48.15.234 11:20, 18 May 2007 (UTC)

You would also need to know the value of g in Heaven. Presumably it is somewhat less than on Earth.--Shantavira 11:44, 18 May 2007 (UTC)

Haha! :-) —Bromskloss 12:01, 18 May 2007 (UTC)

Why would he need to know g? :/ 213.48.15.234 13:19, 18 May 2007 (UTC)

OP wanted to know "how many pounds before stone will collapase or be crushed". This is (partially) dependent on their weight, which is a function of gravity. Judging by the relatively small size of angels' wings, gravity is much less of an issue in Heaven, and the stones will not be as liable to crushing as they would be on Earth, though of course it would still help if the lower courses were made of the stronger varieties of stones. Don't forget some of the above stones are quite brittle, i.e. hardness is not necessarily a measure of their strength.--Shantavira 13:46, 18 May 2007 (UTC)

You could find this in wikipedia anyway. From the first one Jasper, it says it's a variety of quartz, and on the mohs scale it has an Absolute Hardness of 100 found using a sclerometer. I'm sure you could find the relative strengths using the Absolute Hardness scale. Sandman30s 12:18, 18 May 2007 (UTC)

Actually, Monty, the parameter you are looking for is not the hardness but the compressive strength of the materials. --mglg_(talk) 16:19, 18 May 2007 (UTC)

aircraft engine

what are the similarity between turbo fan and turbo prop engine-— Preceding unsigned comment added by 219.64.90.156 (talk • contribs)

Try Turbofan and Turboprop, or Jet engine. The notes for whatever course this is the homework of might also be of use. --YFB ¿ 14:43, 18 May 2007 (UTC)

They both have a turbine at their core. In the turboprop, the jet engine/turbine is geared or otherwise interfaced with a propeller, so the propeller is spinning because a jet engine is giving it power. A turbofan also has a turbine/jet engine at its core, but instead of driving a propeller, it runs a large fan in the front that provides air for the engine and also blows the extra air past it. It's also typically called a 'high bypass jet engine', what people usually are talking about when they say 'turbofan'. This is the kind of engine that a modern jet liner would have. - CHAIRBOY (☎) 14:45, 18 May 2007 (UTC)

Identifying Identical Twins' DNA...How Can One Tell Which Identical Twin May Have Committed A Crime?

--69.124.86.198 15:49, 18 May 2007 (UTC)Identifying Identical Twins

Identical twins have the same genetic material, as the article explains. Friday (talk) 15:52, 18 May 2007 (UTC)

How about good old fashioned fingerprints? You might get lucky and find a SNP (Single nucleotide polymorphism) that is different between the twins but DNA fingerprinting would be useless with the current genetic markers. David D. (Talk) 15:54, 18 May 2007 (UTC)

The evil one

Drilling for Oil

I'm working on a project about oil drilling at ANWR and there's what appears to be an industry specific word I don't understand. In learning about the different studies on the potential for oil at ANWR, the word "play" often appears. It seems to be a reference to a location or possibly some way of categorizing a hierarchy for differing levels of oil field size. I can't find a thorough description of what a "play" is anywhere. Your help is greatly appreciated. Thanks! 161.28.144.36 16:12, 18 May 2007 (UTC)Paul

According to this USGS report, "a play is a volume of rock that contains similar geological parameters (such as petroleum charge, reservoir, and trap) that determine petroleum potential." There's a bunch of stuff that may help clarify if you do a Google search for petroleum play. — Matt Eason ^{(Talk • Contribs)} 16:23, 18 May 2007 (UTC)

Petroleum...duh. I was typing in "oil play" into google and not getting anything worthwhile. Thanks a bundle :) 161.28.144.36 16:31, 18 May 2007 (UTC)Paul

question about multinertia

Hello,i have a question for you guys:

what's a better situation?

driving at 100 M/H against a concrete wall,or driving at 100 M/H against a car,which is driving directly towards your path.

better situation,meaning,which one is least deadly?

thanks for answering

oh and i know that it has to do something with inertia,and the difference of V over the diff of A

see you — Preceding unsigned comment added by 84.192.49.154 (talk • contribs)

One factor is the total speed of the collision. When hitting a wall, the speed is your speed. In a head-on collision, the total speed is the sum of the speed of both vehicles assuming nearly-equal mass and a direct hit. However, that is rarely the case. Going back to the wall, your collision will be rather survivable if you are travelling below 45mph. I don't know of a single vehicle (not including motorcycles) that cannot survive a 45mph impact. As the speed increases, the strength of the cage inside the body and length of the crumple zones plays a major role. The goal is to slow you down over time rather than go from 100mph to 0mph instantly. So, cars are designed to crumple everywhere except where the people sit.

Now, back to the head-on collision. There are many factors involved. Just last weekend, I saw an SUV that hit a little VW Rabbit on the interstate. It wasn't a head-on, but the result was not as most people expect. The back of the rabbit was smashed in and the driver was standing next to it talking on the cell phone. The SUV was on its side, all beat up (obviously rolled). There was a lot of blood coming out of it and two bodies covered in sheets by it. The fire department was cutting as least one other person out of the SUV. The problem is that the SUV is too high and top-heavy. When hitting the little car, it just lifted one tire and flipped. The small car that was low to the ground just crumpled where it was supposed to and skidded to a stop. --Kainaw ^(talk) 17:26, 18 May 2007 (UTC)

Do snakes have eye lids?

My daughter was curious, seriously. Thanks! --Tom 17:20, 18 May 2007 (UTC)

See snakes (search for "eyelids" - it is under Evolution). --Kainaw ^(talk) 17:27, 18 May 2007 (UTC)

Non-linear voltage amplifier

I would like to build an electronic device using only analog components that will allow me to replicate the behavior of the curve in this image. Ideally, I would be able to adjust the rise-time (Adj. 1) and the proportions of the three slopes (Adj. 2 & 3). Could you suggest any circuits that would help me design this device?

--Jcmaco 17:32, 18 May 2007 (UTC)